Methods and Compositions for Efficient Base Calling in Sequencing Reactions

ABSTRACT

The present invention is directed to methods and compositions for acquiring nucleotide sequence information of target sequences. In particular, the present invention provides methods and compositions for improving the efficiency of sequencing reactions by using fewer labels to distinguish between nucleotides and by detecting nucleotides at multiple detection positions in a target sequence.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/094,630 (filed Dec. 2, 2013), which in turn is a continuation of U.S.patent application Ser. No. 12/361,507, (filed Jan. 28, 2009, and issuedas U.S. Pat. No. 8,617,811 on Dec. 31, 2013) which claims benefit ofU.S. Patent Application Nos. 61/024,110 (filed Jan. 28, 2008) and61/024,396 (filed Jan. 29, 2008), each of which is hereby incorporatedby reference in its entirety.

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED AS AN ASCII TEXT FILE

The Sequence Listing written in file 92171-911271_ST25.TXT, created Jun.11, 2014, 7,285 bytes, machine format IBM-PC, MS-Windows operatingsystem, is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Large-scale genomic sequence analysis is a key step toward understandinga wide range of biological phenomena. The need for low-cost,high-throughput sequencing and re-sequencing has led to the developmentof new approaches to sequencing that employ parallel analysis ofmultiple nucleic acid targets simultaneously.

Conventional methods of sequencing are generally restricted todetermining a few tens of nucleotides before signals becomesignificantly degraded, thus placing a significant limit on overallsequencing efficiency. Conventional methods of sequencing are also oftenlimited by signal-to-noise ratios that render such methods unsuitablefor single-molecule sequencing.

It would be advantageous for the field if methods and compositions couldbe designed to increase the efficiency of sequencing reactions as wellas the efficiency of assembling complete sequences from shorter readlengths.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides methods and compositions forbase calling in sequencing reactions.

In one aspect, the present invention provides a method of identifying afirst nucleotide at a detection position of a target sequence. Thismethod includes the step of providing a surface that includes aplurality of concatemers, and each concatemer includes a plurality ofmonomers, and each monomer includes: (i) a first target domain of thetarget sequence; (ii) a first detection position; (iii) a first adaptoradjacent to said first target domain, wherein the first adaptorcomprises a first anchor site. This method further includes the step ofproviding a first sequencing set of sequencing probes. The first set ofsequencing probes includes a first, second, third and fourth probe set.The first probe set includes: (i) a first unique label; (ii) a firstprobe domain complementary to the first target domain; and (iii) a firstunique nucleotide at a first interrogation position. The second probeset includes: (i) a second unique label; (ii) the first probe domain;and (iii) a second unique nucleotide at the first interrogationposition; The third probe set includes: (i) the first and second label;(ii) the first probe domain; and (iii) a third unique nucleotide at thefirst interrogation position. The fourth probe set includes: (i) thefirst probe domain; and (ii) a fourth unique nucleotide at the firstinterrogation position. In this aspect of the invention, the methodfurther includes hybridizing an anchor probe to the first anchor siteand applying the set of sequencing probes to the surface. If asequencing probe from the sequencing set has a unique nucleotide that iscomplementary to the first nucleotide, that sequencing probe hybridizesto the concatemer. The method further includes the step of ligatinghybridized sequencing probes to hybridized anchor probes to formligation products and then identifying the sequencing probes of thoseligation products in order to identify the first nucleotide.

In some embodiments, the present invention provides a method fordetermining an identity of a base at a position in a target nucleic acidcomprising distinguishing four nucleotides from one another in areaction using two labels. In some aspects, the identity of the base inthe target nucleic acid is determined by sequencing-by-synthesis,sequencing by hybridization, sequencing-by-ligation or cPAL.

In some aspects, the identity of a base is determined by: (a) providinglibrary constructs comprising target nucleic acid and at least oneadaptor; (b) hybridizing anchor probes to the adaptors in the libraryconstructs; (c) hybridizing a pool of sequencing probes to the targetnucleic acid, wherein a first sequencing probe identifies a base at aninterrogation position and has a first label, a second sequencing probeidentifies a second base at the interrogation position and has a secondlabel, and a third sequencing probe identifies a third base at theinterrogation position and has both the first and second label or somethird sequencing probes have the first label and some third sequencingprobes have the second label; (d) ligating the sequencing probes to theanchor probes, wherein the sequencing probe that is complementary to thetarget nucleic acid at the interrogated position will ligateefficiently; and (e) determining which sequencing probe if any ligatedto the anchor probe so as to determine a sequence of the target nucleicacid.

In some instances, the unligated sequencing probes are discarded afterstep (d). Also, in some instances, processes (b) through (e) arerepeated until a desired amount of sequence of target nucleic acid isobtained. In yet other instances, the pool of sequencing probescomprises a fourth sequencing probe that identifies a fourth base at theinterrogation position and has no label. For example, in some specificinstances, the G probe is unlabeled or unused and the C probe is labeledwith two colors, and in yet other instances, the T probe is unlabeled orunused and the A probe is labeled with two colors.

In further aspects, the identity of a base is determined by: (a)providing library constructs comprising target nucleic acid and at leastone adaptor, wherein the target nucleic acid has a position to beinterrogated; (b) hybridizing anchor probes to the adaptors in thelibrary constructs; (c) hybridizing a pool of sequencing probes to thetarget nucleic acid, wherein a first sequencing probe identifies a firstbase at the interrogation position and has a first label with a firstintensity, a second sequencing probe identifies a second base at theinterrogation position and has a first label with a second intensity, athird sequencing probe identifies a third base at the interrogationposition and has a second label with a first intensity, and a fourthsequencing probe identifies a fourth base at the interrogation positionand has a second label with a second intensity; (d) ligating thesequencing probes to the anchor probes, wherein the sequencing probethat is complementary to the target nucleic acid at the interrogatedposition will ligate efficiently; and (e) determining which sequencingprobe ligated to the anchor probe so as to determine a sequence of thetarget nucleic acid.

Other methods of the claimed invention provide a method for determiningan identity of two bases at different positions in a target nucleic acidcomprising distinguishing eight nucleotides from one another using twolabels.

In one aspect, the identity of two bases at different positions isdetermined by: (a) providing library constructs comprising targetnucleic acid and at least one adaptor, wherein the target nucleic acidhas a first and a second position to be interrogated; (b) hybridizinganchor probes to the adaptors in the library constructs; (c) hybridizinga pool of sequencing probes to interrogate two positions of the targetnucleic acid, the pool comprising: (i) a first sequencing probe thatidentifies a first base at the first interrogation position comprising afirst label with a first intensity, a second sequencing probe thatidentifies a second base at the first interrogation position comprisinga first label with a second intensity, a third sequencing probe thatidentifies a third base at the first interrogation position comprising afirst label with a third intensity, and a fourth sequencing probe thatidentifies a fourth base at the first interrogation position comprisinga first label with a fourth intensity, and (ii) a first sequencing probethat identifies a first base at the second interrogation positioncomprising a second label with a first intensity, a second basesequencing probe that identifies a second base at the secondinterrogation position comprising a second label with a secondintensity, a third sequencing probe that identifies a third base at thesecond interrogation position comprising a second label with a thirdintensity, and an fourth sequencing probe that identifies a fourth baseat the second interrogation position comprising a second label with afourth intensity; (d) ligating the sequencing probes to the anchorprobes, wherein the sequencing probe that is complementary to the targetnucleic acid at the interrogated positions will ligate efficiently; and(e) determining which sequencing probe ligated to the anchor probe so asto determine a sequence of the target nucleic acid.

Other methods of the claimed invention allow determination of theidentity of two bases at different positions in a target nucleic acidcomprising distinguishing eight nucleotides from one another using fourlabels.

In certain aspects, the methods comprise: (a) providing libraryconstructs comprising target nucleic acid and at least one adaptor; (b)hybridizing anchor probes to the adaptors in the library constructs; (c)hybridizing a pool of sequencing probes to interrogate two positions ofthe target nucleic acid, the pool comprising: (i) a first set ofsequencing probes to interrogate a first position on the target nucleicacid comprising a first sequencing probe having a first label, a secondsequencing probe having a second label, and a third sequencing probehaving both the first and second labels or some third sequencing probeshave the first label and some third sequencing probes have the secondlabel; and (ii) a second set of sequencing probes to interrogate asecond position in the target nucleic acid comprising a first sequencingprobe having a third label, a second sequencing probe having a fourthlabel, and a third sequencing probe having both the third and fourthlabels or some third sequencing probes have the third label and somethird sequencing probes have the fourth label; (d) ligating thesequencing probes to the anchor probes, wherein the sequencing probesthat are complementary to the target nucleic acid at the interrogationpositions will ligate efficiently to the anchor probes; and (e)determining which sequencing probes ligated to the anchor probes so asto determine a sequence of the target nucleic acid.

In some aspects of these methods, both sets of sequencing probes ligateto the same anchor. In yet other aspects, the library constructscomprise at least one or more different adaptors and hybridization sitesfor at least two different anchor probes, and the 3′ end of one anchorprobe is used for ligation with a 5′ end of the first set of sequencingprobes and the 5′ end of another anchor probe is used for ligation with3′ end of the second set of sequencing probes. In such a case, the firstset of sequencing probes can ligate to the first anchor probe but notthe second anchor probe and the second set of sequencing probes canligate to the second anchor probe but not the first anchor probe. Insome aspects, the unligated sequencing probes are discarded after step(d). Also, in some aspects, processes (b) through (e) are repeated untila desired amount of sequence of target nucleic acid is obtained. In yetother aspects, the pool of sequencing probes comprises one or morefourth sequencing probes with no label.

The claimed invention also provides a method for determining an identityof four bases at different positions in a target nucleic acid comprisingdistinguishing sixteen nucleotides from one another using four labels.

Some aspects of methods of the invention include (a) providing libraryconstructs comprising target nucleic acid and at least one adaptor; (b)hybridizing anchor probes to the adaptors in the library constructs; (c)hybridizing a pool of sequencing probes to interrogate four positions ofthe target nucleic acid, the pool comprising: (i) a first set ofsequencing probes that interrogates a first position comprising a firstsequencing probe having a first label, a second sequencing probe havinga second label, and a third sequencing probe having both the first andsecond labels or some third sequencing probes have the first label andsome third sequencing probes have the second label, wherein eachsequencing probe of the first set interrogates a different base at thefirst position; (ii) a second set of sequencing probes that interrogatesa second position comprising a first sequencing probe having a firstdissociable label, a second sequencing probe having a second dissociablelabel, and a third sequencing probe having both the first and seconddissociable labels or some third sequencing probes have the firstdisassociable label and some third sequencing probes have the seconddisassociable label, wherein each sequencing probe of the second setinterrogates a different base at the second position; (iii) a third setof sequencing probes that interrogates a third position comprising afirst sequencing probe having a third label, a second sequencing probehaving a fourth label, and a third sequencing probe having both thethird and fourth labels or some third sequencing probes have the thirdlabel and some third sequencing probes have the fourth label, whereineach sequencing probe of the third set interrogates a different base atthe third position; (iv) a fourth set of sequencing probes thatinterrogates a fourth position comprising a first sequencing probehaving a third dissociable label, a second sequencing probe having afourth dissociable label, and a third sequencing probe having both thethird and fourth dissociable labels or some third sequencing probes havethe third disassociable label and some third sequencing probes have thefourth disassociable label, wherein each sequencing probe of the fourthset interrogates a different base at the fourth position; (d) ligatingthe sequencing probes to the anchor probes, wherein the sequencingprobes that are complementary to the target nucleic acid at theinterrogated positions will efficiently ligate to the anchor probes; (e)detecting the labels of the sequencing probes ligated to the anchorprobes so as to determine a sequence of the target nucleic acid; (f)disassociating the disassociable labels in the second and fourth sets ofsequencing probes; (g) detecting the labels of the sequencing probesfrom the first and third sets; and (h) determining which labels weredisassociated and which labels remained, so as to determine a sequenceof the target nucleic acid.

In further aspects processes (b) through (h) are repeated until adesired amount of sequence of target nucleic acid is obtained. Also insome aspects, the pool of sequencing probes may comprise one or morefourth sequencing probes with no label. In various aspects of thismethod, the disassociable labels disassociate by virtue of varyingmelting temperatures, and in yet other aspect, the disassociable labelsdisassociate by one or more cleavage reactions.

Yet other methods for determining an identity of four bases at differentpositions comprise: (a) providing library constructs comprising targetnucleic acid and at least one adaptor; (b) hybridizing anchor probes tothe adaptors in the library constructs; (c) hybridizing a pool ofsequencing probes to interrogate four positions of the target nucleicacid, the pool comprising: (i) a first set of sequencing probes thatinterrogates a first position of the target nucleic acid, the setcomprising a first sequencing probe having a first label with a firstintensity, a second sequencing probe having a first label with a secondintensity, and a third sequencing probe having a first label with athird intensity, wherein each sequencing probe of the first setinterrogates a different base at the first position; (ii) a second setof sequencing probes that interrogates a second position of the targetnucleic acid, the set comprising a first sequencing probe having asecond label with a first intensity, a second sequencing probe having asecond label with a second intensity, and a third sequencing probehaving a second label with a third intensity, wherein each sequencingprobe of the second set interrogates a different base at the secondposition; (iii) a third set of sequencing probes that interrogates athird position of the target nucleic acid, the set comprising a firstsequencing probe having a third label with a first intensity, a secondsequencing probe having a third label with a second intensity, and athird sequencing probe having a third label with a third intensity,wherein each sequencing probe of the third set interrogates a differentbase at the third position; and (iv) a fourth set of sequencing probesthat interrogates a fourth position of the target nucleic acid,comprising a first sequencing probe having a fourth label with a firstintensity, a second sequencing probe having a fourth label with a secondintensity, and a third sequencing probe having a fourth label with athird intensity, wherein each sequencing probe of the fourth setinterrogates a different base at the fourth position; (d) ligating thesequencing probes to the anchor probes, wherein the sequencing probesthat are complementary to the target nucleic acid at the interrogatedpositions will efficiently ligate to the anchor probes; (e) detectingthe intensity of each label of the sequencing probes ligated to theanchor probes so as to determine a sequence of the target nucleic acid.

The present invention also provides a pool of sequencing probes tointerrogate a position in a target nucleic acid, comprising a firstsequencing probe having a first label, a second sequencing probe havinga second label, a third sequencing probe having a first and second labelon one molecule or some third sequencing probes have the first label andsome third sequencing probes have the second label, wherein each probeidentifies a different base at the position of a target nucleic acid. Insome aspects, this pool of sequencing proves further comprises a fourthprobe without a label.

In some embodiments, the present invention provides a pool of sequencingprobes to interrogate a position in a target nucleic acid, comprising afirst sequencing probe having a first label with a first intensity, asecond sequencing probe having a first label with a second intensity, athird sequencing probe having a second label with a first intensity, anda fourth sequencing probe having a second label with a second intensity,wherein each probe identifies a different base at the position of atarget nucleic acid.

Also, in some aspects there is provided a pool of sequencing probes tointerrogate a position in a target nucleic acid comprising a firstsequencing probe having a first disassociable label, a second sequencingprobe having a second disassociable label, and a third sequencing probehaving both the first and second disassociable labels, wherein eachprobe identifies a different base at the position of a target nucleicacid. In some variations, the labels are disassociable by varyingtemperatures, and in other variations, the labels are disassociable bycleavage.

The described technology provides in one aspect a method for determininga sequence of a target nucleic acid comprising: (a) providing libraryconstructs comprising target nucleic acid and at least one adaptor; (b)hybridizing at least first and second anchor probes to the at least oneadaptor in the library constructs; (c) hybridizing labeled sequencingprobes to the target nucleic acid; (d) ligating the labeled sequencingprobes to the anchor probes, wherein the labeled sequencing probes thatare complementary to the target nucleic acid will efficiently ligate tothe anchor probes; (e) detecting the labels of the ligated sequencingprobes; (f) providing a first invader oligonucleotide having a sequencecomplementary to the ligated first anchor probe; (g) allowing the firstinvader oligonucleotide to disrupt hybridization between the ligatedfirst anchor probe and the library constructs by forming a complex withthe ligated first anchor probe; (h) discarding the complex; and (i)detecting the labels of the remaining ligated sequencing probes todetermine a sequence of a target nucleic acid.

In some aspects, processes (b) through (i) are repeated until a desiredamount of sequence of target nucleic acid is obtained. In yet otheraspects, the library constructs comprise at least four differentadaptors, at least four different anchor probes are hybridized to theadaptors, and at least four different invader oligonucleotidessubstantially complementary to the four different anchor probes areprovided. Additionally, in some aspects the method further comprisesdetermining a sequence of the target nucleic acid by subtracting thelabel detected in (e) from the labels detected in (i). Also, in someaspects, the invader oligonucleotide is complementary to a portion ofthe sequencing probe.

Additionally, in some aspects of the methods of the claimed invention,the anchor probe comprises an anchor portion complementary to a portionof the adaptor, the anchor portion of the anchor probe is flanked by atail portion; and wherein the invader oligonucleotide has a tail portionsubstantially complementary to the tail portion of the anchor probe.Alternatively or in addition, the anchor probe may further comprise adegenerate portion for binding target nucleic acid. Yet in otheraspects, the invader oligonucleotide comprises a loop; and in someaspects, the loop is substantially complementary to a loop of an anchorprobe.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key or essentialfeatures of the claimed subject matter, nor is it intended to be used tolimit the scope of the claimed subject matter. Other features, details,utilities, and advantages of the claimed subject matter will be apparentfrom the following written Detailed Description including those aspectsillustrated in the accompanying drawings and defined in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an embodiment of sequencingmethods of the invention. Sequence legend: anchor primer 130 (SEQ IDNO:6); array-immobilized template strand 100 (SEQ ID NO:10).

FIG. 2 is an illustration of exemplary embodiments of probe sets of theinvention.

FIG. 3 is an illustration of exemplary embodiments of probe sets of theinvention.

FIG. 4 is an illustration of exemplary embodiments of probe sets of theinvention.

FIG. 5 is a schematic illustration of an embodiment of sequencingmethods of the invention. Sequence legend: 501 (SEQ ID NO:11); 502 (SEQID NO:12); 504 (SEQ ID NO:11, SEQ ID NO:12); 507 (SEQ ID NO:13, SEQ IDNO:14).

FIGS. 6A and 6B provide schematic illustrations of an embodiment ofsequencing methods of the invention (A) and exemplary probe sets of usein such an embodiment (B). Sequence legend: 701 (SEQ ID NO:21); 702 (SEQID NO:22); 703 (SEQ ID NO:23).

FIG. 7 is a schematic illustration of an embodiment of sequencingmethods of the invention.

FIG. 8 is a schematic illustration of an embodiment of sequencingmethods of the invention. Sequence legend: 812 (SEQ ID NO:24); 816 (SEQID NO:25); 819 (SEQ ID NO:26).

FIG. 9 provides sequences of exemplary adaptors of the invention.Sequence legend: (A) (SEQ ID NO:1); (B) (SEQ ID NO:2); (C) (SEQ IDNO:3); (D) (SEQ ID NO:4); (E) (SEQ ID NO:5).

FIG. 10 provides (A) sequences of exemplary adaptors of the inventionand (B) a schematic illustration of exemplary functional elements of anadaptor. Sequence legend: 1102 (SEQ ID NO:16); 1104 (SEQ ID NO:17); 1108(SEQ ID NO:19); 1106 (SEQ ID NO:18); 1110 (SEQ ID NO:20).

FIG. 11 is a schematic illustration of an embodiment of sequencingmethods of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The practice of the present invention may employ, unless otherwiseindicated, conventional techniques and descriptions of organicchemistry, polymer technology, molecular biology (including recombinanttechniques), cell biology, biochemistry, and immunology, which arewithin the skill of the art. Such conventional techniques includepolymer array synthesis, hybridization, ligation, and detection ofhybridization using a label. Specific illustrations of suitabletechniques can be had by reference to the example herein below. However,other equivalent conventional procedures can, of course, also be used.Such conventional techniques and descriptions can be found in standardlaboratory manuals such as Genome Analysis: A Laboratory Manual Series(Vols. I-IV), Using Antibodies: A Laboratory Manual, Cells: A LaboratoryManual, PCR Primer: A Laboratory Manual, and Molecular Cloning: ALaboratory Manual (all from Cold Spring Harbor Laboratory Press),Stryer, L. (1995) Biochemistry (4th Ed.) Freeman, N.Y., Gait,“Oligonucleotide Synthesis: A Practical Approach” 1984, IRL Press,London, Nelson and Cox (2000), Lehninger, Principles of Biochemistry3^(rd) Ed., W. H. Freeman Pub., New York, N.Y. and Berg et al. (2002)Biochemistry, 5^(th) Ed., W. H. Freeman Pub., New York, N.Y., all ofwhich are herein incorporated in their entirety by reference for allpurposes.

Note that as used herein and in the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a polymerase”refers to one agent or mixtures of such agents, and reference to “themethod” includes reference to equivalent steps and methods known tothose skilled in the art, and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. All publications mentionedherein are incorporated herein by reference for the purpose ofdescribing and disclosing devices, compositions, formulations andmethodologies which are described in the publication and which might beused in connection with the presently described invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges is also encompassed within the invention, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either both ofthose included limits are also included in the invention.

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the present invention. However,it will be apparent to one of skill in the art that the presentinvention may be practiced without one or more of these specificdetails. In other instances, well-known features and procedures wellknown to those skilled in the art have not been described in order toavoid obscuring the invention.

Although the present invention is described primarily with reference tospecific embodiments, it is also envisioned that other embodiments willbecome apparent to those skilled in the art upon reading the presentdisclosure, and it is intended that such embodiments be contained withinthe present inventive methods.

I. Overview

The present invention is directed to methods and compositions foridentifying and detecting nucleotides in a target sequence. In general,the methods are directed to new methods and improvements to technologybased on the use of arrays of DNA nanoballs, sometimes referred hereinas “DNBs”, which can be used for extremely efficient sequencing (as wellas expression analysis and genotyping). These technologies are generallydescribed in U.S. application Ser. Nos. 11/679,124; 11/981,761;11/981,661; 11/981,605; 11/981,793; 11/981,804; 11/451,691; 11/981,607;11/981,767; 11/982,467; 11/451,692; 12/335,168; 11/541,225; 11/927,356;11/927,388; 11/938,096; 11/938,106; 10/547,214; 11/981,730; 11/981,685;11/981,797; 12/252,280; 11/934,695; 11/934,697; 11/934,703; 12/265,593;12/266,385; 11/938,213; 11/938,221; 12/325,922; 12/329,365; 12/335,188and 12/359,165, all of which are hereby incorporated by reference intheir entirety for all purposes and particularly for all disclosurerelated to DNBs, methods of making DNBs and methods of using DNBs.However, as will be appreciated by those in the art, the techniquesdescribed herein can be used on other platforms, e.g. other nucleic acidarray systems, including both solid and liquid phase systems. Thus,while much of the description herein is directed to the discussion ofDNB arrays, any and all of the techniques described herein can beapplied to other platforms, in any combination.

Thus, the present invention is generally directed to the methods thatallow the determination of a plurality of bases using a number of labels(e.g. fluorophores) where the number of labels is less than the numberof bases that are determined at each cycle. For example, using themethods described herein, a sequencing reaction can be done in whichwherein 4 bases can be distinguished using probe sets labeled with onlytwo dyes. The ability to read two or more bases per sequencing readcycle reduces the time and cost of sequencing experiments, allowinglarge numbers of sequences (including whole genomes) to be detected andidentified without a prohibitive increase in time and cost.

Accordingly, methods for nucleic acid identification and detection usingcompositions and methods of the present invention include extracting andfragmenting target nucleic acids from a sample. These fragmented nucleicacids are used to produce target nucleic acid templates that generallyinclude one or more adaptors. The target nucleic acid templates aresubjected to amplification methods to form nucleic acid concatemers,also referred to herein as nucleic acid “nanoballs” and “amplicons”. Insome situations, these nanoballs are disposed on a surface. Sequencingapplications are performed on the nucleic acid nanoballs of theinvention, usually through sequencing by ligation techniques, includingcombinatorial probe anchor ligation (“cPAL”) methods, which aredescribed in further detail below.

Sequencing applications of the invention will in general utilizesequencing probes that include a domain that is complementary to adomain of the target sequence as well as a unique nucleotide at aninterrogation position. The methods described herein are applicable to anumber of sequencing techniques, including sequencing by ligationtechniques, sequencing by extension (SBE), such as described in U.S.Pat. Nos. 6,210,891; 6,828,100, 6,833,246; 6,911,345; Margulies, et al.(2005), Nature 437:376-380 and Ronaghi, et al. (1996), Anal. Biochem.242:84-89, each of which is hereby incorporated by reference in itsentirety for all purposes and in particular for all teachings related tosequencing by extension, sequencing by hybridization, such as themethods described in U.S. Pat. No. 6,401,267, which is herebyincorporated by reference in its entirety for all purposes and inparticular for all teachings related to sequencing by hybridizationmethods. In general, these methods rely on sequencing probes thathybridize to a domain of the target nucleic acid. Such sequencing probeswill in general stably hybridize to regions of the target sequence towhich the sequencing probes are perfectly complementary. Conventionalmethods of sequencing utilize four sequencing probes that utilize fourdifferent labels to distinguish among sequencing probes for a particularnucleotide at a particular position in the target sequence—i.e., aunique label for each unique nucleotide at a specific position. (Or,alternatively, for SBE reactions, the sequencing probe is identical foreach reaction but the nucleotide(s) for addition each have a uniquelabel). The present invention provides methods and compositions thatimprove the efficiency and/or cost of identifying a base in a targetsequence by distinguishing between the four possible nucleotides usingfewer than four unique labels.

In some cases, sequencing applications of the invention use sets ofsequencing probes which are labeled in such a way as to distinguishbetween four nucleotides using only two different labels. One example ofsuch a set of probes is illustrated in FIG. 2. In FIG. 2, set 202 is anexample of a probe set that is useful in methods where two labels areused to read four bases. As shown in 202, the A probe is labeled with afirst label (identified as C1), the T probe is labeled with a secondlabel (C2), the C probe is labeled with both the first and the secondlabel (C1+C2), and the G probe is not labeled. In sequencingapplications utilizing a probe set such as that pictured in 202, thepresence of the G probe is detected when no label can be detected. Thelabels on probes such as those pictured in FIG. 2 can be any kind ofdetectable label known in the art as described more fully below, and inspecific cases, fluorescent labels are used.

In some cases, sequencing applications using the nucleic acid nanoballsof the invention can detect more than two bases in a target nucleic acidby utilizing probes whose ligation to anchor probes is controlled. Forexample, sequencing probes can be “fixed” in orientation by blocking oneend such that only sequencing probes that hybridize to a particular sideof an adaptor, or in a particular orientation with respect to the anchorprobe, will be able to ligate to the anchor probe. For example, in FIG.2, set 204 is premised along the same lines as set 202, except that withset 204, four different labels are used to distinguish between 8different nucleotides—i.e., to identify which base is present at twodifferent locations in a target sequence. As discussed above anddescribed in further detail below, nucleic acid nanoballs of theinvention comprise repeating units of target sequence and adaptors. Inspecific examples of sequencing applications of the invention, four ofthe probes in set 204 are 3′ probes, i.e., they can hybridize tolocations of the target sequence 3′ to an adaptor, whereas the otherfour probes are 5′ probes and hybridize only to locations 5′ to anadaptor. Similar to the labeling scheme of set 202 discussed above, the5′ probes of set 204 has an A probe labeled with a first label (C1), a Tprobe labeled with a second label (C2), a C probe labeled with the firstand second labels (C1+C2) and a G probe that has no label. In addition,the 3′ probes of set 204 has an A probe labeled with a third label (C3),a T probe labeled with a fourth label (C4), a C probe labeled with boththe third and fourth label (C3+C4), and again the G probe is unlabeled.By structuring the probes in this way, a set such as probe set **204 canbe used to identify the nucleotide at two different positions of atarget sequence.

In certain cases, the nucleotides at four different positions of atarget sequence in a nucleic acid nanoball are identified by using fourprobe sets in a single sequencing cycle to read two bases from each sideof an adaptor. One example of such a sequencing application isillustrated in FIG. 6A, which shows an exemplary portion of a nucleicacid nanoball 602 with adaptors on each of the 5′ and 3′ ends (shaded“b”s) and target nucleic acid to be sequenced in between the adaptors(i.e., in between the shaded regions). In addition, sequencing probesare shown that would allow for reading of the four bases from 5′ and 3′of the two adaptors shown in two cycles. In the method of sequencingillustrated in FIGS. 6A and 6B, probe sets of the type shown in FIG. 2at 204 are used; however, four probe sets are used in a single reactionto read two bases from each side. In FIGS. 6A and 6B, “G”, “T”, “A” and“C” are specific nucleotide bases, and “N”s are universal or degeneratebases. In a first cycle of sequencing, four probes sets 620 are used. Asequencing probe that would identify the G in the target nucleic acidimmediately 3′ to the end of the 5′ adaptor is shown at 604(CNNNNNN-C1/C2). Such a sequencing probe would be part of a first set622: CNNNNNN-C1/C2; ANNNNNN-C1; TNNNNNN-C2 and GNNNNNN (see FIG. 6B forthe probe sets that would be used in each of the two rounds ofsequencing). The sequencing probe that would identify the T in thetarget nucleic acid two bases from the 3′ end of the 5′ adaptor is shownat 606 (NANNNNN‡C1), and would be part of a second set 624: NANNNNN‡C1;NTNNNNN‡C2; NGNNNNN; and NCNNNNN‡C1C2, where the symbol “‡” denotes acleavage site). A broad variety of cleavable moieties are available inthe art of solid phase and microarray oligonucleotide synthesis,including photocleavable moieties (see, e.g., Pon, R. (1993), MethodsMol. Biol. 20:465-496; Verma et al. (1998), Annu. Rev. Biochem.67:99-134; and U.S. Pat. Nos. 5,739,386 and 5,700,642). Again, using a Gprobe in this instance is optional, since the G probe does not have alabel.

A sequencing probe that would identify the C in the target nucleic acidimmediately 5′ to the end of the 3′ adaptor is shown at 612 (NNNNNNG).Such a sequencing probe would be part of a third set 626: NNNNNNG;C3/C4-NNNNNC; C31-NNNNNA; and C4-NNNNNT. The sequencing probe that wouldidentify the A in the target nucleic acid two bases from the 5′ end ofthe 3′ adaptor is shown at 614 (C4‡NNNNTN), and would be part of afourth set 628: C4‡NNNNTN; C3‡NNNNAN; NNNNNGN; and C3C4‡NNNNCN, again,where the symbol “‡” denotes a cleavage site. The first, second, thirdand fourth sequencing probe sets are used together to sequence fourbases at a time in the following manner: Anchor probes are allowed tohybridize to the adaptors in the library constructs after which (orsimultaneously) all four sets of sequencing probes are added and allowedto hybridize to the target nucleic acid. The adjacently-hybridizedanchor probes and sequencing probes may then be ligated to one anotherif the sequencing probe is complementary to the target nucleic acid inthe library construct. An extensive wash is performed to eliminateunligated sequencing probes. Two sequencing probes will ligate to theanchor probes that hybridized to the 5′ adaptor (one sequencing probefrom the first sequencing probe set (604) and one sequencing probe fromthe second sequencing probe set (606)), and two sequencing probes willligate to anchor probes that hybridized to the 3′ adaptor (onesequencing probe from the third sequencing probe set (612) and onesequencing probe from the fourth sequencing probe set (614)). It shouldbe noted that more than one sequencing probe will not ligate to a singleanchor probe, but about half of the 5′ anchor probes will ligate tosequencing probes from the first set, and about half of the 5′ anchorprobes will ligate to sequencing probes from the second set. Similarly,about half of the 3′ anchor probes will ligate to sequencing probes fromthe third set, and about half of the 5′ anchor probes will ligate tosequencing probes from the fourth set.

The fluorescent signal for the first read out in this hypothetical wouldbe C1+C2+C1 from the 5′ side and no color (from the G sequencingprobe)+C4 from the 3′ side. The sequencing reaction mix is thensubjected to cleaving at the “‡” site, eliminating the fluorescentsignal from the sequencing probes interrogating the bases in the targetnucleic acid two nucleotides from the ligation junction (i.e.,sequencing probes from the second and fourth sequencing probe sets). Awash is then performed, and the fluorescent signal is read again. Thefluorescent signal for the second read out in this hypothetical would beC1+C2 from the 5′ side and no color from the 3′ side. That is, thestrong C1 signal contributed by the NANNNNN‡CL sequencing probe (606)and the C4 signal contributed by the C2‡NNNNNTN sequencing probe (614)will have disappeared. The disappearance of a strong C1 signal indicatesthat a T is two bases from the 3′ end of the 5′ adaptor (the Asequencing probe from the second set ligated to the anchor probe). Thedisappearance of the C4 signal indicates that an A is two bases from the5′ end of the 3′ adaptor (the T sequencing probe from the fourth setligated to the anchor probe). The remaining C1+C2 signal indicates thata G is in the first position in the target nucleic acid immediately 3′to the end of the 5′ adaptor (the C sequencing probe from the first setligated to the anchor probe) and that there is no color at all from thethird sequencing probe set indicates that a C is the first base in thetarget nucleic acid immediately 5′ to the end of the 3′ adaptor (the Gsequencing probe from the third set ligated to the anchor probe).

Further examples of sequencing methods using combinations of probe setsaccording to the present invention are described in further detailbelow.

II. Nucleic Acid Nanoballs and Arrays

Compositions of the invention include nucleic acid templates,concatemers generated from such nucleic acid templates, as well assubstrates comprising a surface with a plurality of such concatemersdisposed on that surface (also referred to herein as “arrays”). Suchcompositions are described in U.S. application Ser. Nos. 11/679,124;11/981,761; 11/981,661; 11/981,605; 11/981,793; 11/981,804; 11/451,691;11/981,607; 11/981,767; 11/982,467; 11/451,692; 12/335,168; 11/541,225;11/927,356; 11/927,388; 11/938,096; 11/938,106; 10/547,214; 11/981,730;11/981,685; 11/981,797; 12/252,280; 11/934,695; 11/934,697; 11/934,703;12/265,593; 12/266,385; 11/938,213; 11/938,221; 12/325,922; 12/329,365;12/335,188 and 12/359,165, all of which are hereby incorporated byreference in their entirety for all purposes and particularly for alldisclosure related to nucleic acid templates, concatemers and arraysaccording to the present invention.

In one aspect, the present invention provides nucleic acid templatescomprising target nucleic acids and multiple interspersed adaptors, alsoreferred to herein as “library constructs,” “circular templates”,“circular constructs”, “target nucleic acid templates”, and othergrammatical equivalents. The nucleic acid template constructs of theinvention are assembled by inserting adaptors molecules at amultiplicity of sites throughout each target nucleic acid. Theinterspersed adaptors permit acquisition of sequence information frommultiple sites in the target nucleic acid consecutively orsimultaneously.

The term “target nucleic acid” refers to a nucleic acid of interest. Inone aspect, target nucleic acids of the invention are genomic nucleicacids, although other target nucleic acids can be used, including mRNA(and corresponding cDNAs, etc.). Target nucleic acids include naturallyoccurring or genetically altered or synthetically prepared nucleic acids(such as genomic DNA from a mammalian disease model). Target nucleicacids can be obtained from virtually any source and can be preparedusing methods known in the art. For example, target nucleic acids can bedirectly isolated without amplification, isolated by amplification usingmethods known in the art, including without limitation polymerase chainreaction (PCR), strand displacement amplification (SDA), multipledisplacement amplification (MDA), rolling circle amplification (RCA),rolling circle amplification (RCR) and other amplification (includingwhole genome amplification) methodologies. Target nucleic acids may alsobe obtained through cloning, including but not limited to cloning intovehicles such as plasmids, yeast, and bacterial artificial chromosomes.

In some aspects, the target nucleic acids comprise mRNAs or cDNAs. Incertain embodiments, the target DNA is created using isolatedtranscripts from a biological sample. Isolated mRNA may be reversetranscribed into cDNAs using conventional techniques, again as describedin Genome Analysis: A Laboratory Manual Series (Vols. I-IV) or MolecularCloning: A Laboratory Manual.

Target nucleic acids can be obtained from a sample using methods knownin the art. As will be appreciated, the sample may comprise any numberof substances, including, but not limited to, bodily fluids (including,but not limited to, blood, urine, serum, lymph, saliva, anal and vaginalsecretions, perspiration and semen, of virtually any organism, withmammalian samples being preferred and human samples being particularlypreferred); environmental samples (including, but not limited to, air,agricultural, water and soil samples); biological warfare agent samples;research samples (i.e. in the case of nucleic acids, the sample may bethe products of an amplification reaction, including both target andsignal amplification as is generally described in PCT/US99/01705, suchas PCR amplification reaction); purified samples, such as purifiedgenomic DNA, RNA, proteins, etc.; raw samples (bacteria, virus, genomicDNA, etc.); as will be appreciated by those in the art, virtually anyexperimental manipulation may have been done on the sample. In oneaspect, the nucleic acid constructs of the invention are formed fromgenomic DNA. In certain embodiments, the genomic DNA is obtained fromwhole blood or cell preparations from blood or cell cultures.

In an exemplary embodiment, genomic DNA is isolated from a targetorganism. By “target organism” is meant an organism of interest and aswill be appreciated, this term encompasses any organism from whichnucleic acids can be obtained, particularly from mammals, includinghumans, although in some embodiments, the target organism is a pathogen(for example for the detection of bacterial or viral infections).Methods of obtaining nucleic acids from target organisms are well knownin the art. Samples comprising genomic DNA of humans find use in manyembodiments. In some aspects such as whole genome sequencing, about 20to about 1,000,0000 or more genome-equivalents of DNA are preferablyobtained to ensure that the population of target DNA fragmentssufficiently covers the entire genome. The number of genome equivalentsobtained may depend in part on the methods used to further preparefragments of the genomic DNA for use in accordance with the presentinvention.

The target nucleic acids used to make templates of the invention may besingle stranded or double stranded, as specified, or contain portions ofboth double stranded or single stranded sequence. Depending on theapplication, the nucleic acids may be DNA (including genomic and cDNA),RNA (including mRNA and rRNA) or a hybrid, where the nucleic acidcontains any combination of deoxyribo- and ribo-nucleotides, and anycombination of bases, including uracil, adenine, thymine, cytosine,guanine, inosine, xathanine hypoxathanine, isocytosine, isoguanine, etc.

By “nucleic acid” or “oligonucleotide” or “polynucleotide” orgrammatical equivalents herein means at least two nucleotides covalentlylinked together. A nucleic acid of the present invention will generallycontain phosphodiester bonds, although in some cases, as outlined below(for example in the construction of primers and probes such as labelprobes), nucleic acid analogs are included that may have alternatebackbones, comprising, for example, phosphoramide (Beaucage et al.,Tetrahedron 49(10):1925 (1993) and references therein; Letsinger, J.Org. Chem. 35:3800 (1970); Sprinzl et al., Eur. J. Biochem. 81:579(1977); Letsinger et al., Nucl. Acids Res. 14:3487 (1986); Sawai et al,Chem. Lett. 805 (1984), Letsinger et al., J. Am. Chem. Soc. 110:4470(1988); and Pauwels et al., Chemica Scripta 26:141 91986)),phosphorothioate (Mag et al., Nucleic Acids Res. 19:1437 (1991); andU.S. Pat. No. 5,644,048), phosphorodithioate (Briu et al., J. Am. Chem.Soc. 111:2321 (1989), O-methylphosphoroamidite linkages (see Eckstein,Oligonucleotides and Analogues: A Practical Approach, Oxford UniversityPress), and peptide nucleic acid (also referred to herein as “PNA”)backbones and linkages (see Egholm, J. Am. Chem. Soc. 114:1895 (1992);Meier et al., Chem. Int. Ed. Engl. 31:1008 (1992); Nielsen, Nature,365:566 (1993); Carlsson et al., Nature 380:207 (1996), all of which areincorporated by reference). Other analog nucleic acids include thosewith bicyclic structures including locked nucleic acids (also referredto herein as “LNA”), Koshkin et al., J. Am. Chem. Soc. 120:13252 3(1998); positive backbones (Denpcy et al., Proc. Natl. Acad. Sci. USA92:6097 (1995); non-ionic backbones (U.S. Pat. Nos. 5,386,023,5,637,684, 5,602,240, 5,216,141 and U.S. Pat. No. 4,469,863; Kiedrowshiet al., Angew. Chem. Intl. Ed. English 30:423 (1991); Letsinger et al.,J. Am. Chem. Soc. 110:4470 (1988); Letsinger et al., Nucleoside &Nucleotide 13:1597 (1994); Chapters 2 and 3, ASC Symposium Series 580,“Carbohydrate Modifications in Antisense Research”, Ed. Y. S. Sanghuiand P. Dan Cook; Mesmaeker et al., Bioorganic & Medicinal Chem. Lett.4:395 (1994); Jeffs et al., J. Biomolecular NMR 34:17 (1994);Tetrahedron Lett. 37:743 (1996)) and non-ribose backbones, includingthose described in U.S. Pat. Nos. 5,235,033 and 5,034,506, and Chapters6 and 7, ASC Symposium Series 580, “Carbohydrate Modifications inAntisense Research”, Ed. Y. S. Sanghui and P. Dan Cook. Nucleic acidscontaining one or more carbocyclic sugars are also included within thedefinition of nucleic acids (see Jenkins et al., Chem. Soc. Rev. (1995)pp 169 176). Several nucleic acid analogs are described in Rawls, C & ENews Jun. 2, 1997 page 35. “Locked nucleic acids” (LNA™) are alsoincluded within the definition of nucleic acid analogs. LNAs are a classof nucleic acid analogues in which the ribose ring is “locked” by amethylene bridge connecting the 2′-0 atom with the 4′-C atom. All ofthese references are hereby expressly incorporated by reference in theirentirety for all purposes and in particular for all teachings related tonucleic acids. These modifications of the ribose-phosphate backbone maybe done to increase the stability and half-life of such molecules inphysiological environments. For example, PNA:DNA and LNA-DNA hybrids canexhibit higher stability and thus may be used in some embodiments.

The nucleic acid templates of the invention comprise target nucleicacids and adaptors. As used herein, the term “adaptor” refers to anoligonucleotide of known sequence. Adaptors of use in the presentinvention may include a number of elements. The types and numbers ofelements (also referred to herein as “features”, “functional elements”and grammatical equivalents) included in an adaptor will depend on theintended use of the adaptor. Adaptors of use in the present inventionwill generally include without limitation sites for restrictionendonuclease recognition and/or cutting, particularly Type IIsrecognition sites that allow for endonuclease binding at a recognitionsite within the adaptor and cutting outside the adaptor as describedbelow, sites for primer binding (for amplifying the nucleic acidconstructs) or anchor primer (sometimes also referred to herein as“anchor probes”) binding (for sequencing the target nucleic acids in thenucleic acid constructs), nickase sites, and the like. In someembodiments, adaptors will comprise a single recognition site for arestriction endonuclease, whereas in other embodiments, adaptors willcomprise two or more recognition sites for one or more restrictionendonucleases. As outlined herein, the recognition sites are frequently(but not exclusively) found at the termini of the adaptors, to allowcleavage of the double stranded constructs at the farthest possibleposition from the end of the adaptor. Adaptors of use in the inventionare described herein and in U.S. application Ser. Nos. 11/679,124;11/981,761; 11/981,661; 11/981,605; 11/981,793; 11/981,804; 11/451,691;11/981,607; 11/981,767; 11/982,467; 11/451,692; 12/335,168; 11/541,225;11/927,356; 11/927,388; 11/938,096; 11/938,106; 10/547,214; 11/981,730;11/981,685; 11/981,797; 12/252,280; 11/934,695; 11/934,697; 11/934,703;12/265,593; 12/266,385; 11/938,213; 11/938,221; 12/325,922; 12/329,365;12/335,188 and 12/359,165, all of which are hereby incorporated byreference in their entirety for all purposes and particularly for alldisclosure related to adaptors and target nucleic acid templatescomprising adaptors.

In some embodiments, adaptors of the invention have a length of about 10to about 250 nucleotides, depending on the number and size of thefeatures included in the adaptors. In certain embodiments, adaptors ofthe invention have a length of about 50 nucleotides. In furtherembodiments, adaptors of use in the present invention have a length ofabout 20 to about 225, about 30 to about 200, about 40 to about 175,about 50 to about 150, about 60 to about 125, about 70 to about 100, andabout 80 to about 90 nucleotides.

In further embodiments, adaptors may optionally include elements suchthat they can be ligated to a target nucleic acid as two “arms”. One orboth of these arms may comprise an intact recognition site for arestriction endonuclease, or both arms may comprise part of arecognition site for a restriction endonuclease. In the latter case,circularization of a construct comprising a target nucleic acid boundedat each termini by an adaptor arm will reconstitute the entirerecognition site.

In still further embodiments, adaptors of use in the invention willcomprise different anchor binding sites (also referred to herein as“anchor sites”) at their 5′ and the 3′ ends. As described furtherherein, such anchor binding sites can be used in sequencingapplications, including the combinatorial probe anchor ligation (cPAL)method of sequencing, described herein and in U.S. application Ser. Nos.11/679,124; 11/981,761; 11/981,661; 11/981,605; 11/981,793; 11/981,804;11/451,691; 11/981,607; 11/981,767; 11/982,467; 11/451,692; 12/335,168;11/541,225; 11/927,356; 11/927,388; 11/938,096; 11/938,106; 10/547,214;11/981,730; 11/981,685; 11/981,797; 12/252,280; 11/934,695; 11/934,697;11/934,703; 12/265,593; 12/266,385; 11/938,213; 11/938,221; 12/325,922;12/329,365; 12/335,188 and 12/359,165, all of which are herebyincorporated by reference in their entirety for all purposes andparticularly for all disclosure related to, all of which are herebyincorporated by reference in their entirety, and particularly for alldisclosure related to sequencing by ligation.

In one aspect, adaptors of the invention are interspersed adaptors. By“interspersed adaptors” is meant herein oligonucleotides that areinserted at spaced locations within the interior region of a targetnucleic acid. In one aspect, “interior” in reference to a target nucleicacid means a site internal to a target nucleic acid prior to processing,such as circularization and cleavage, that may introduce sequenceinversions, or like transformations, which disrupt the ordering ofnucleotides within a target nucleic acid.

“Interspersed adaptors” can be inserted such that they interrupt acontiguous target sequence, thus conferring a spatial and distanceorientation between the target sequences. That is, as outlined hereinand in the incorporated applications, using endonucleases that cutoutside of the recognition sequence allows the precise insertion (vialigation) of adaptors at defined intervals within the target sequence.This facilitates sequence reconstruction and alignment, as sequence runsof 10 bases each from a single adaptor can allow 20, 30, 40, etc. basesto be read without alignment, per se.

The nucleic acid template constructs of the invention contain multipleinterspersed adaptors inserted into a target nucleic acid, and in aparticular orientation. As discussed further herein, the target nucleicacids are produced from nucleic acids isolated from one or more cells,including one to several million cells. These nucleic acids are thenfragmented using mechanical or enzymatic methods.

The target nucleic acid that becomes part of a nucleic acid templateconstruct of the invention may have interspersed adaptors inserted atintervals within a contiguous region of the target nucleic acids atpredetermined positions. The intervals may or may not be equal. In someaspects, the accuracy of the spacing between interspersed adaptors maybe known only to an accuracy of one to a few nucleotides. In otheraspects, the spacing of the adaptors is known, and the orientation ofeach adaptor relative to other adaptors in the library constructs isknown. That is, in many embodiments, the adaptors are inserted at knowndistances, such that the target sequence on one terminus is contiguousin the naturally occurring genomic sequence with the target sequence onthe other terminus. For example, in the case of a Type IIs restrictionendonuclease that cuts 16 bases from the recognition site, if therecognition site is located 3 bases into the adaptor, the endonucleasecuts 13 bases from the end of the adaptor. Upon the insertion of asecond adaptor, the target sequence “upstream” of the adaptor and thetarget sequence “downstream” of the adaptor are actually contiguoussequences in the original target sequence. Thus, the interspersedadaptors of the present invention are truly “inserted” into a targetsequence rather than simply appended to the ends of fragments randomlygenerated through enzymatic and mechanical methods.

Although the embodiments of the invention described herein are generallydescribed in terms of circular nucleic acid template constructs, it willbe appreciated that nucleic acid template constructs may also be linear.Furthermore, nucleic acid template constructs of the invention may besingle- or double-stranded, with the latter being preferred in someembodiments.

In further embodiments, nucleic acid templates formed from a pluralityof genomic fragments can be used to create a library of nucleic acidtemplates. Such libraries of nucleic acid templates will in someembodiments encompass target nucleic acids that together encompass allor part of an entire genome. That is, by using a sufficient number ofstarting genomes (e.g. cells), combined with random fragmentation, theresulting target nucleic acids of a particular size that are used tocreate the circular templates of the invention sufficiently “cover” thegenome, although as will be appreciated, on occasion, bias may beintroduced inadvertently to prevent the entire genome from beingrepresented.

The nucleic acid template constructs of the invention comprise multipleinterspersed adaptors, and in some aspects, these interspersed adaptorscomprise one or more recognition sites for restriction endonucleases. Infurther aspect, the adaptors comprise recognition sites for Type IIsendonucleases. Type-IIs endonucleases are generally commerciallyavailable and are well known in the art. Like their Type-IIcounterparts, Type-IIs endonucleases recognize specific sequences ofnucleotide base pairs within a double stranded polynucleotide sequence.Upon recognizing that sequence, the endonuclease will cleave thepolynucleotide sequence, generally leaving an overhang of one strand ofthe sequence, or “sticky end.” Type-IIs endonucleases also generallycleave outside of their recognition sites; the distance may be anywherefrom about 2 to 30 nucleotides away from the recognition site dependingon the particular endonuclease. Some Type-IIs endonucleases are “exactcutters” that cut a known number of bases away from their recognitionsites. In some embodiments, Type IIs endonucleases are used that are not“exact cutters” but rather cut within a particular range (e.g. 6 to 8nucleotides). Generally, Type IIs restriction endonucleases of use inthe present invention have cleavage sites that are separated from theirrecognition sites by at least six nucleotides (i.e. the number ofnucleotides between the end of the recognition site and the closestcleavage point). Exemplary Type IIs restriction endonucleases include,but are not limited to, Eco57M I, Mme I, Acu I, Bpm I, BceA I, Bbv I,BciV I, BpuE I, BseM II, BseR I, Bsg I, BsmF I, BtgZ I, Eci I, EcoP15 I,Eco57M I, Fok I, Hga I, Hph I, Mbo II, Mnl I, SfaN I, TspDT I, TspDW I,Taq II, and the like. In some exemplary embodiments, the Type IIsrestriction endonucleases used in the present invention are AcuI, whichhas a cut length of about 16 bases with a 2-base 3′ overhang and EcoP15,which has a cut length of about 25 bases with a 2-base 5′ overhang. Aswill be discussed further below, the inclusion of a Type IIs site in theadaptors of the nucleic acid template constructs of the inventionprovides a tool for inserting multiple adaptors in a target nucleic acidat a defined location.

As will be appreciated, adaptors may also comprise other elements,including recognition sites for other (non-Type IIs) restrictionendonucleases, including Type I and Type III restriction endonucleases,as well as Type II endonucleases (including IIB, IIE, IIG, IIM, and anyother enzymes known in the art), primer binding sites for amplificationas well as binding sites for probes used in sequencing reactions(“anchor probes”), described further herein. Type III endonucleases,similar to the Type IIs endonucleases, cut at sites outside of theirrecognition sites. These enzymes, as for many of the enzymes recitedherein, may also be used in to control the inactivation and activationof restriction endonuclease recognition sites through methylation, asdescribed in U.S. application Ser. Nos. 12/265,593; 12/266,385;12/329,365; and 12/335,188, each of which is herein incorporated byreference in its entirety for all purposes and in particular for allteachings related to the insertion of multiple adaptors and the controlover recognition sites for restriction endonucleases contained in suchadaptors.

In one aspect, adaptors of use in the invention have sequences as shownin FIGS. 9 and 10 (SEQ ID NOs. 1-9). In further aspects, adaptors of usein the invention may comprise one or more of the sequences illustratedin FIGS. 9 and 10. As will be appreciated, sequences that have at least65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,and 99% sequence identity to the sequences provided in FIGS. 1 and 2 arealso encompassed by the present invention. As identified in theschematic of one of the adaptors in FIG. 10B, adaptors can comprisemultiple functional features, including recognition sites for Type IIsrestriction endonucleases (1003 and 1006), sites for nickingendonucleases (1004) as well as sequences that can influence secondarycharacteristics, such as bases to disrupt hairpins (1001 and 1002).

In further embodiments, adaptors of use in the invention containstabilizing sequences. By the term “stabilizing sequences” or“stabilization sequences” herein is meant nucleic acid sequences thatfacilitate DNB formation and/or stability. For example, stabilizationsequences can allow the formation of secondary structures within theDNBs of the invention. Complementary sequences, including palindromicsequences, find particular use in the invention. In some cases, it ispossible to use nucleic acid binding proteins and their recognitionsequences as stabilization sequences, or crosslinking components as ismore fully described below. Multiple configurations of stabilizingsequences can be used in the invention, and will depend in part upon thenumbers of adaptors used in the constructs, the desired structures ofthe amplicon, and the placement of the binding region in each constructrelative to the stabilizing sequences. Stabilizing sequences (alsoreferred to as “secondary structure sequences”) are described in U.S.patent application Ser. Nos. 11/679,124; 11/981,761; 11/981,661;11/981,605; 11/981,793; 11/981,804; 11/451,691; 11/981,607; 11/981,767;11/982,467; 11/451,692; 12/335,168; 11/541,225; 11/927,356; 11/927,388;11/938,096; 11/938,106; 10/547,214; 11/981,730; 11/981,685; 11/981,797;12/252,280; 11/934,695; 11/934,697; 11/934,703; 12/265,593; 12/266,385;11/938,213; 11/938,221; 12/325,922; 12/329,365; 12/335,188 and12/359,165, all of which are hereby incorporated by reference in theirentirety for all purposes and particularly for all disclosure related tostabilizing and secondary structure sequences.

In some embodiments, concatemers of the invention are disposed on thesurface of a substrate. Methods for making such compositions (alsoreferred to herein as “arrays”) are described in U.S. application Ser.Nos. 11/679,124; 11/981,761; 11/981,661; 11/981,605; 11/981,793;11/981,804; 11/451,691; 11/981,607; 11/981,767; 11/982,467; 11/451,692;12/335,168; 11/541,225; 11/927,356; 11/927,388; 11/938,096; 11/938,106;10/547,214; 11/981,730; 11/981,685; 11/981,797; 12/252,280; 11/934,695;11/934,697; 11/934,703; 12/265,593; 12/266,385; 11/938,213; 11/938,221;12/325,922; 12/329,365; 12/335,188 and 12/359,165, all of which arehereby incorporated by reference in their entirety for all purposes andparticularly for all disclosure related to arrays of concatemers andmethods of making such arrays.

In certain embodiments, arrays of the invention comprise concatemersthat are randomly disposed on an unpatterned or patterned surface. Incertain embodiments, arrays of the invention comprise concatemers thatare disposed in known locations on an unpatterned or patterned surface.Arrays of the invention may comprise concatemers fixed to surface by avariety of techniques, including covalent attachment and non-covalentattachment. In one embodiment, a surface may include capture probes thatform complexes, e.g., double stranded duplexes, with component of apolynucleotide molecule, such as an adaptor oligonucleotide. In otherembodiments, capture probes may comprise oligonucleotide clamps, or likestructures, that form triplexes with adaptors, as described in Gryaznovet al, U.S. Pat. No. 5,473,060, which is hereby incorporated in itsentirety for all purposes and in particular for all teachings related toarrays.

III. Sequencing Methods

The present invention provides methods and compositions for identifyingmultiple bases in a target nucleic acid by utilizing sets of probes thatcan distinguish between four possible bases at one or more positions ina target sequence using fewer than four labels in a set of sequencingprobes. The methods of the present invention allow for multiple basecalls per sequencing cycle, thus reducing the time and cost ofsequencing and detection of sequences of target nucleic acids.

Although the following description of sequencing applications of thepresent invention is provided in terms of DNBs, it will be appreciatedthat these methods can be applied to any nucleic acid targets and arenot necessarily limited to concatemers comprising target sequence andadaptors.

Methods of using DNBs in accordance with the present invention includesequencing and detecting specific sequences in target nucleic acids(e.g., detecting particular target sequences (e.g. specific genes)and/or identifying and/or detecting SNPs). The methods described hereincan also be used to detect nucleic acid rearrangements and copy numbervariation. Nucleic acid quantification, such as digital gene expression(i.e., analysis of an entire transcriptome—all mRNA present in a sample)and detection of the number of specific sequences or groups of sequencesin a sample, can also be accomplished using the methods describedherein. Methods of using DNBs in sequencing reactions and in thedetection of particular target sequences are also described in U.S.patent application Ser. Nos. 11/679,124; 11/981,761; 11/981,661;11/981,605; 11/981,793; 11/981,804; 11/451,691; 11/981,607; 11/981,767;11/982,467; 11/451,692; 12/335,168; 11/541,225; 11/927,356; 11/927,388;11/938,096; 11/938,106; 10/547,214; 11/981,730; 11/981,685; 11/981,797;12/252,280; 11/934,695; 11/934,697; 11/934,703; 12/265,593; 12/266,385;11/938,213; 11/938,221; 12/325,922; 12/329,365; 12/335,188 and12/359,165, each of which is herein incorporated by reference in itsentirety for all purposes and in particular for all teachings relatedconducting sequencing reactions on DNBs of the invention. As will beappreciated, any of the sequencing methods described herein and known inthe art can be applied to nucleic acid templates and/or DNBs of theinvention in solution or to nucleic acid templates and/or DNBs disposedon a surface and/or in an array.

In one aspect, sequences of DNBs are identified using sequencing methodsknown in the art, including, but not limited to, hybridization-basedmethods, such as disclosed in Drmanac, U.S. Pat. Nos. 6,864,052;6,309,824; and 6,401,267; and Drmanac et al, U.S. patent publication2005/0191656, and sequencing by synthesis methods, e.g. Nyren et al,U.S. Pat. No. 6,210,891; Ronaghi, U.S. Pat. No. 6,828,100; Ronaghi et al(1998), Science, 281: 363-365; Balasubramanian, U.S. Pat. No. 6,833,246;Quake, U.S. Pat. No. 6,911,345; Li et al, Proc. Natl. Acad. Sci., 100:414-419 (2003); Smith et al, PCT publication WO 2006/074351; andligation-based methods, e.g. Shendure et al (2005), Science, 309:1728-1739, Macevicz, U.S. Pat. No. 6,306,597, wherein each of thesereferences is herein incorporated by reference in its entirety for allpurposes and in particular teachings regarding the figures, legends andaccompanying text describing the compositions, methods of using thecompositions and methods of making the compositions, particularly withrespect to sequencing.

In some embodiments, nucleic acid templates of the invention, as well asDNBs generated from those templates, are used in sequencing by synthesismethods. The efficiency of sequencing by synthesis methods utilizingnucleic acid templates of the invention is increased over conventionalsequencing by synthesis methods utilizing nucleic acids that do notcomprise multiple interspersed adaptors. Rather than a single long read,nucleic acid templates of the invention allow for multiple short readsthat each start at one of the adaptors in the template. Such short readsconsume fewer labeled dNTPs, thus saving on the cost of reagents. Inaddition, sequencing by synthesis reactions can be performed on DNBarrays, which provide a high density of sequencing targets as well asmultiple copies of monomeric units. Such arrays provide detectablesignals at the single molecule level while at the same time providing anincreased amount of sequence information, because most or all of the DNBmonomeric units will be extended without losing sequencing phase. Thehigh density of the arrays also reduces reagent costs—in someembodiments the reduction in reagent costs can be from about 30 to about40% over conventional sequencing by synthesis methods. In someembodiments, the interspersed adaptors of the nucleic acid templates ofthe invention provide a way to combine about two to about ten standardreads if inserted at distances of from about 30 to about 100 bases apartfrom one another. In such embodiments, the newly synthesized strandswill not need to be stripped off for further sequencing cycles, thusallowing the use of a single DNB array through about 100 to about 400sequencing by synthesis cycles.

IIIA. Sequencing by Ligation Using cPAL Methods

In one aspect, the present invention provides methods for identifyingsequences of DNBs that utilize a sequencing by ligation method. Inspecific embodiments, the sequencing by ligation method used is acombinatorial probe anchor ligation (cPAL) method. Generally, cPALinvolves identifying a nucleotide at a detection position in a targetnucleic acid by detecting a probe ligation product formed by ligation ofat least one anchor probe and at least one sequencing probe. Suchmethods are described in U.S. patent application Ser. Nos. 11/679,124;11/981,761; 11/981,661; 11/981,605; 11/981,793; 11/981,804; 11/451,691;11/981,607; 11/981,767; 11/982,467; 11/451,692; 12/335,168; 11/541,225;11/927,356; 11/927,388; 11/938,096; 11/938,106; 10/547,214; 11/981,730;11/981,685; 11/981,797; 12/252,280; 11/934,695; 11/934,697; 11/934,703;12/265,593; 12/266,385; 11/938,213; 11/938,221; 12/325,922; 12/329,365;12/335,188 and 12/359,165, each of which is herein incorporated byreference in its entirety for all purposes and in particular for allteachings related to cPAL sequencing methods. Methods of the inventioncan be used to sequence a portion or the entire sequence of the targetnucleic acid contained in a DNB, and many DNBs that represent a portionor all of a genome.

As discussed further herein, every DNB comprises repeating monomericunits, each monomeric unit comprising one or more adaptors and a targetnucleic acid. The target nucleic acid comprises a plurality of detectionpositions. The term “detection position” refers to a position in atarget sequence for which sequence information is desired. As will beappreciated by those in the art, generally a target sequence hasmultiple detection positions for which sequence information is required,for example in the sequencing of complete genomes as described herein.In some cases, for example in SNP analysis, it may be desirable to justread a single SNP in a particular area.

The present invention provides methods of sequencing by ligation thatutilize a combination of anchor probes and sequencing probes. By“sequencing probe” as used herein is meant an oligonucleotide that isdesigned to provide the identity of a nucleotide at a particulardetection position of a target nucleic acid. Sequencing probes hybridizeto domains within target sequences, e.g. a first sequencing probe mayhybridize to a first target domain, and a second sequencing probe mayhybridize to a second target domain. The terms “first target domain” and“second target domain” or grammatical equivalents herein means twoportions of a target sequence within a nucleic acid which is underexamination. The first target domain may be directly adjacent to thesecond target domain, or the first and second target domains may beseparated by an intervening sequence, for example an adaptor. The terms“first” and “second” are not meant to confer an orientation of thesequences with respect to the 5′-3′ orientation of the target sequence.For example, assuming a 5′-3′ orientation of the complementary targetsequence, the first target domain may be located either 5′ to the seconddomain, or 3′ to the second domain. Sequencing probes can overlap, e.g.a first sequencing probe can hybridize to the first 6 bases adjacent toone terminus of an adaptor, and a second sequencing probe can hybridizeto the 3rd-9th bases from the terminus of the adaptor (for example whenan anchor probe has three degenerate bases). Alternatively, a firstsequencing probe can hybridize to the 6 bases adjacent to the “upstream”terminus of an adaptor and a second sequencing probe can hybridize tothe 6 bases adjacent to the “downstream” terminus of an adaptor.

Sequencing probes will generally comprise a number of degenerate basesand a specific nucleotide at a specific location within the probe toquery the detection position (also referred to herein as an“interrogation position”).

In general, pools of sequencing probes are used when degenerate basesare used. That is, a probe having the sequence “NNNANN” is actually aset of probes of having all possible combinations of the four nucleotidebases at five positions (i.e., 1024 sequences) with an adenosine at the6th position. (As noted herein, this terminology is also applicable toadaptor probes: for example, when an adaptor probe has “three degeneratebases”, for example, it is actually a set of adaptor probes comprisingthe sequence corresponding to the anchor site, and all possiblecombinations at 3 positions, so it is a pool of 64 probes).

In some embodiments, for each interrogation position, four differentlylabeled pools can be combined in a single pool and used in a sequencingstep. Thus, in any particular sequencing step, 4 pools are used, eachwith a different specific base at the interrogation position and with adifferent label corresponding to the base at the interrogation position.That is, sequencing probes are also generally labeled such that aparticular nucleotide at a particular interrogation position isassociated with a label that is different from the labels of sequencingprobes with a different nucleotide at the same interrogation position.For example, four pools can be used: NNNANN-dye1, NNNTNN-dye2,NNNCNN-dye3 and NNNGNN-dye4 in a single step, as long as the dyes areoptically resolvable. In some embodiments, for example for SNPdetection, it may only be necessary to include two pools, as the SNPcall will be either a C or an A, etc. Similarly, some SNPs have threepossibilities. Alternatively, in some embodiments, if the reactions aredone sequentially rather than simultaneously, the same dye can be done,just in different steps: e.g. the NNNANN-dye1 probe can be used alone ina reaction, and either a signal is detected or not, and the probeswashed away; then a second pool, NNNTNN-dye1 can be introduced.

In any of the sequencing methods described herein, sequencing probes mayhave a wide range of lengths, including about 3 to about 25 bases. Infurther embodiments, sequencing probes may have lengths in the range ofabout 5 to about 20, about 6 to about 18, about 7 to about 16, about 8to about 14, about 9 to about 12, and about 10 to about 11 bases.

Sequencing probes of the present invention are designed to becomplementary, and in general, perfectly complementary, to a sequence ofthe target sequence such that hybridization of a portion target sequenceand probes of the present invention occurs. In particular, it isimportant that the interrogation position base and the detectionposition base be perfectly complementary and that the methods of theinvention do not result in signals unless this is true.

In many embodiments, sequencing probes are perfectly complementary tothe target sequence to which they hybridize; that is, the experimentsare run under conditions that favor the formation of perfectbasepairing, as is known in the art. As will be appreciated by those inthe art, a sequencing probe that is perfectly complementary to a firstdomain of the target sequence could be only substantially complementaryto a second domain of the same target sequence; that is, the presentinvention relies in many cases on the use of sets of probes, forexample, sets of hexamers, that will be perfectly complementary to sometarget sequences and not to others.

In some embodiments, depending on the application, the complementaritybetween the sequencing probe and the target need not be perfect; theremay be any number of base pair mismatches, which will interfere withhybridization between the target sequence and the single strandednucleic acids of the present invention. However, if the number ofmismatches is so great that no hybridization can occur under even theleast stringent of hybridization conditions, the sequence is not acomplementary target sequence. Thus, by “substantially complementary”herein is meant that the sequencing probes are sufficientlycomplementary to the target sequences to hybridize under normal reactionconditions. However, for most applications, the conditions are set tofavor probe hybridization only if perfectly complementarity exists.Alternatively, sufficient complementarity is required to allow theligase reaction to occur; that is, there may be mismatches in some partof the sequence but the interrogation position base should allowligation only if perfect complementarity at that position occurs.

In some cases, in addition to or instead of using degenerate bases inprobes of the invention, universal bases which hybridize to more thanone base can be used. For example, inosine can be used. Any combinationof these systems and probe components can be utilized.

Sequencing probes of use in methods of the present invention are usuallydetectably labeled. By “label” or “labeled” herein is meant that acompound has at least one element, isotope or chemical compound attachedto enable the detection of the compound. In general, labels of use inthe invention include without limitation isotopic labels, which may beradioactive or heavy isotopes, magnetic labels, electrical labels,thermal labels, colored and luminescent dyes, enzymes and magneticparticles as well. Dyes of use in the invention may be chromophores,phosphors or fluorescent dyes, which due to their strong signals providea good signal-to-noise ratio for decoding. Sequencing probes may also belabeled with quantum dots, fluorescent nanobeads or other constructsthat comprise more than one molecule of the same fluorophore. Labelscomprising multiple molecules of the same fluorophore will generallyprovide a stronger signal and will be less sensitive to quenching thanlabels comprising a single molecule of a fluorophore. It will beunderstood that any discussion herein of a label comprising afluorophore will apply to labels comprising single and multiplefluorophore molecules.

Many embodiments of the invention include the use of fluorescent labels.Suitable dyes for use in the invention include, but are not limited to,fluorescent lanthanide complexes, including those of Europium andTerbium, fluorescein, rhodamine, tetramethylrhodamine, eosin,erythrosin, coumarin, methyl-coumarins, pyrene, Malacite green,stilbene, Lucifer Yellow, CASCADE BLUE®, Texas Red, and others describedin the 6th Edition of the Molecular Probes Handbook by Richard P.Haugland, hereby expressly incorporated by reference in its entirety forall purposes and in particular for its teachings regarding labels of usein accordance with the present invention. Commercially availablefluorescent dyes for use with any nucleotide for incorporation intonucleic acids include, but are not limited to: Cy3, Cy5, (AmershamBiosciences, Piscataway, N.J., USA), fluorescein, tetramethylrhodamine-,TEXAS RED®, CASCADE BLUE®, BODIPY® FL-14, BODIPY®R, BODIPY® TR-14,RHODAMINE GREEN™, OREGON GREEN® 488, BODIPY® 630/650, BODIPY® 650/665-,ALEXA FLUOR® 488, ALEXA FLUOR® 532, ALEXA FLUOR® 568, ALEXA FLUOR® 594,ALEXA FLUOR® 546 (Molecular Probes, Inc. Eugene, Oreg., USA), QUASAR®570, QUASAR® 670, Cal Red 610 (BioSearch Technologies, Novato, Ca).Other fluorophores available for post-synthetic attachment include,inter alia, ALEXA FLUOR® 350, ALEXA FLUOR® 532, ALEXA FLUOR® 546, ALEXAFLUOR® 568, ALEXA FLUOR® 594, ALEXA FLUOR® 647, BODIPY® 493/503, BODIPY®FL, BODIPY® R6G, BODIPY® 530/550, BODIPY® TMR, BODIPY® 558/568, BODIPY®558/568, BODIPY® 564/570, BODIPY® 576/589, BODIPY® 581/591, BODIPY®630/650, BODIPY® 650/665, CASCADE BLUE®, CASCADE YELLOW™, Dansyl,lissamine rhodamine B, Marina Blue, Oregon Green 488, Oregon Green 514,Pacific Blue, rhodamine 6G, rhodamine green, rhodamine red,tetramethylrhodamine, Texas Red (available from Molecular Probes, Inc.,Eugene, Oreg., USA), and Cy2, Cy3.5, Cy5.5, and Cy7 (AmershamBiosciences, Piscataway, N.J. USA, and others). In some embodiments, thelabels used include fluoroscein, Cy3, Texas Red, Cy5, QUASAR® 570,QUASAR® 670 and Cal Red 610 are used in methods of the presentinvention.

Labels can be attached to nucleic acids to form the labeled sequencingprobes of the present invention using methods known in the art, and to avariety of locations of the nucleosides. For example, attachment can beat either or both termini of the nucleic acid, or at an internalposition, or both. For example, attachment of the label may be done on aribose of the ribose-phosphate backbone at the 2′ or 3′ position (thelatter for use with terminal labeling), in one embodiment through anamide or amine linkage. Attachment may also be made via a phosphate ofthe ribose-phosphate backbone, or to the base of a nucleotide. Labelscan be attached to one or both ends of a probe or to any one of thenucleotides along the length of a probe.

Sequencing probes are structured differently depending on theinterrogation position desired. For example, in the case of sequencingprobes labeled with fluorophores, a single position within eachsequencing probe will be correlated with the identity of the fluorophorewith which it is labeled. Generally, the fluorophore molecule will beattached to the end of the sequencing probe that is opposite to the endtargeted for ligation to the anchor probe.

By “anchor probe” as used herein is meant an oligonucleotide designed tobe complementary to at least a portion of an adaptor, referred to hereinas “an anchor site”. Adaptors can contain multiple anchor sites forhybridization with multiple anchor probes, as described herein. Asdiscussed further herein, anchor probes of use in the present inventioncan be designed to hybridize to an adaptor such that at least one end ofthe anchor probe is flush with one terminus of the adaptor (either“upstream” or “downstream”, or both). In further embodiments, anchorprobes can be designed to hybridize to at least a portion of an adaptor(a first adaptor site) and also at least one nucleotide of the targetnucleic acid adjacent to the adaptor (“overhangs”). As illustrated inFIG. 5, anchor probe 502 comprises a sequence complementary to a portionof the adaptor. Anchor probe 502 also comprises four degenerate bases atone terminus. This degeneracy allows for a portion of the anchor probepopulation to fully or partially match the sequence of the targetnucleic acid adjacent to the adaptor and allows the anchor probe tohybridize to the adaptor and reach into the target nucleic acid adjacentto the adaptor regardless of the identity of the nucleotides of thetarget nucleic acid adjacent to the adaptor. This shift of the terminalbase of the anchor probe into the target nucleic acid shifts theposition of the base to be called closer to the ligation point, thusallowing the fidelity of the ligase to be maintained. In general,ligases ligate probes with higher efficiency if the probes are perfectlycomplementary to the regions of the target nucleic acid to which theyare hybridized, but the fidelity of ligases decreases with distance awayfrom the ligation point. Thus, in order to minimize and/or preventerrors due to incorrect pairing between a sequencing probe and thetarget nucleic acid, it can be useful to maintain the distance betweenthe nucleotide to be detected and the ligation point of the sequencingand anchor probes. By designing the anchor probe to reach into thetarget nucleic acid, the fidelity of the ligase is maintained whilestill allowing a greater number of nucleotides adjacent to each adaptorto be identified. Although the embodiment illustrated in FIG. 5 is onein which the sequencing probe hybridizes to a region of the targetnucleic acid on one side of the adaptor, it will be appreciated thatembodiments in which the sequencing probe hybridizes on the other sideof the adaptor are also encompassed by the invention. In FIG. 5, “N”represents a degenerate base and “B” represents nucleotides ofundetermined sequence. As will be appreciated, in some embodiments,rather than degenerate bases, universal bases may be used. It willappreciated that FIG. 5 illustrates only one exemplary embodiment ofsequencing by ligation methods of use in the present invention. Furtherembodiments are described in U.S. application Ser. Nos. 11/679,124;11/981,761; 11/981,661; 11/981,605; 11/981,793; 11/981,804; 11/451,691;11/981,607; 11/981,767; 11/982,467; 11/451,692; 12/335,168; 11/541,225;11/927,356; 11/927,388; 11/938,096; 11/938,106; 10/547,214; 11/981,730;11/981,685; 11/981,797; 12/252,280; 11/934,695; 11/934,697; 11/934,703;12/265,593; 12/266,385; 11/938,213; 11/938,221; 12/325,922; 12/329,365;and 12/335,188, each of which is hereby incorporated in its entirety forall purposes and in particular for all teachings related to differentembodiments of sequencing by ligation using combinations of anchor andsequencing probes.

Anchor probes of the invention may comprise any sequence that allows theanchor probe to hybridize to a DNB, generally to an adaptor of a DNB.Such anchor probes may comprise a sequence such that when the anchorprobe is hybridized to an adaptor, the entire length of the anchor probeis contained within the adaptor. In some embodiments, anchor probes maycomprise a sequence that is complementary to at least a portion of anadaptor and also comprise degenerate bases that are able to hybridize totarget nucleic acid regions adjacent to the adaptor. In some exemplaryembodiments, anchor probes are hexamers that comprise 3 bases that arecomplementary to an adaptor and 3 degenerate bases. In some exemplaryembodiments, anchor probes are 8-mers that comprise 3 bases that arecomplementary to an adaptor and 5 degenerate bases. In further exemplaryembodiments, particularly when multiple anchor probes are used, a firstanchor probe comprises a number of bases complementary to an adaptor atone end and degenerate bases at another end, whereas a second anchorprobe comprises all degenerate bases and is designed to ligate to theend of the first anchor probe that comprises degenerate bases. It willbe appreciated that these are exemplary embodiments, and that a widerange of combinations of known and degenerate bases can be used toproduce anchor probes of use in accordance with the present invention.

The present invention provides sequencing by ligation methods foridentifying sequences of DNBs. In certain aspects, the sequencing byligation methods of the invention include providing differentcombinations of anchor probes and sequencing probes, which, whenhybridized to adjacent regions on a DNB, can be ligated to form probeligation products. The probe ligation products are then detected, whichprovides the identity of one or more nucleotides in the target nucleicacid. By “ligation” as used herein is meant any method of joining two ormore nucleotides to each other. Ligation can include chemical as well asenzymatic ligation. In general, the sequencing by ligation methodsdiscussed herein utilize enzymatic ligation by ligases. Such ligasesinvention can be the same or different than ligases discussed above forcreation of the nucleic acid templates. Such ligases include withoutlimitation DNA ligase I, DNA ligase II, DNA ligase III, DNA ligase IV,E. coli DNA ligase, T4 DNA ligase, T4 RNA ligase 1, T4 RNA ligase 2, T7ligase, T3 DNA ligase, and thermostable ligases (including withoutlimitation Taq ligase) and the like. As discussed above, sequencing byligation methods often rely on the fidelity of ligases to only joinprobes that are perfectly complementary to the nucleic acid to whichthey are hybridized. This fidelity will decrease with increasingdistance between a base at a particular position in a probe and theligation point between the two probes. As such, conventional sequencingby ligation methods can be limited in the number of bases that can beidentified. The present invention increases the number of bases that canbe identified by using multiple probe pools, as is described furtherherein.

A variety of hybridization conditions may be used in the sequencing byligation methods of sequencing as well as other methods of sequencingdescribed herein. These conditions include high, moderate and lowstringency conditions; see for example Maniatis et al., MolecularCloning: A Laboratory Manual, 2d Edition, 1989, and Short Protocols inMolecular Biology, ed. Ausubel, et al, which are hereby incorporated byreference. Stringent conditions are sequence-dependent and will bedifferent in different circumstances. Longer sequences hybridizespecifically at higher temperatures. An extensive guide to thehybridization of nucleic acids is found in Tijssen, Techniques inBiochemistry and Molecular Biology—Hybridization with Nucleic AcidProbes, “Overview of principles of hybridization and the strategy ofnucleic acid assays,” (1993). Generally, stringent conditions areselected to be about 5-10° C. lower than the thermal melting point (Tm)for the specific sequence at a defined ionic strength and pH. The Tm isthe temperature (under defined ionic strength, pH and nucleic acidconcentration) at which 50% of the probes complementary to the targethybridize to the target sequence at equilibrium (as the target sequencesare present in excess, at Tm, 50% of the probes are occupied atequilibrium). Stringent conditions can be those in which the saltconcentration is less than about 1.0 M sodium ion, typically about 0.01to 1.0 M sodium ion concentration (or other salts) at pH 7.0 to 8.3 andthe temperature is at least about 30° C. for short probes (e.g. 10 to 50nucleotides) and at least about 60° C. for long probes (e.g. greaterthan 50 nucleotides). Stringent conditions may also be achieved with theaddition of helix destabilizing agents such as formamide. Thehybridization conditions may also vary when a non-ionic backbone, i.e.PNA is used, as is known in the art. In addition, cross-linking agentsmay be added after target binding to cross-link, i.e. covalently attach,the two strands of the hybridization complex.

In any of the embodiments described herein, sequencing probes of theinvention can be modified such that they hybridize to the targetsequence and ligate to an adjacent anchor probe in a desiredorientation. For example, in order to ensure that a set of sequencingprobes will only ligate to an anchor probe such that their interrogationposition is two bases 5′ of the anchor probe, one end of the sequencingprobes can be blocked such that ligation can only occur at the desiredend. Such methods of modifying nucleic acids, including nucleic acidsequencing probes, to control for orientation and direction of ligationare known in the art and are also described in U.S. application Ser.Nos. 12/329,365 and 12/335,188, which are both herein incorporated byreference in their entirety for all purposes and in particular for allteachings related to controlling ligation of nucleic acid molecules toeach other in a desired orientation.

IIIB. Increasing Efficiency in Base Calling in Sequencing Reactions

In one aspect, the present invention provides methods and compositionsfor improving the efficiency in base calling in sequencing reactions. By“base calling” herein is meant the ability to read a nucleotide at aparticular detection position and is understood by those in the art. Insome embodiments, the present invention provides methods andcompositions for distinguishing among four different nucleotides usingfewer than four labels. In further embodiments, the present inventionprovides methods and compositions for detecting two or more bases persequencing reaction cycle. Such embodiments serve to improve theefficiency of base calling, because the reduction in the number oflabels required in a particular sequencing reaction and the increase inthe number of bases that can be read in a particular sequencing reactioncycle serves to reduce costs and time associated with sequencing targetnucleic acids. Such a savings in time and costs can be of particularbenefit when sequencing large numbers of nucleic acids, as is involvedin applications such as whole genome sequencing.

As discussed above, conventional methods of sequencing will generallyuse four different labels to distinguish between the four possible basesat a specific location in a target sequence. The present inventionutilizes fewer than four unique labels to distinguish between the fourpossible bases, thus increasing the speed and decreasing the cost ofsequencing reactions. Using fewer than four labels to distinguishbetween four nucleotides also provides the ability to detect multiplebases in a sequencing reaction cycle without needing to use more thanfour labels. This is of particular use at the current state of the art,as most labels, particularly fluorescent labels, are harder todistinguish when more than four wavelengths (e.g. four colors) are used.

Although the following description is provided in terms of sequencing byligation methods, particularly cPAL, it will be appreciated that themethods and compositions described herein can be used with anysequencing method known in the art, including sequencing by extension(also known as sequencing by synthesis) and sequencing by hybridization.For example, it will be apparent to one of skill in the art that probesets such as those described in further detail below can be used insequencing by extension reactions, with the variation that rather thansequencing probes, the labels will generally be attached to dNTPs. Suchvariations on the methods and compositions described herein could bemade using standard and routine techniques by one of skill in the artand are therefore encompassed by the present invention.

In one embodiment, sequencing applications of the invention use sets ofsequencing probes which are labeled in such a way as to distinguishbetween four nucleotides at a single detection position using only twodifferent labels. Generally, in this embodiment, only two labels areused, generally fluorophores.

One example of this embodiment is illustrated in FIG. 2. In FIG. 2, set202 is an example of a probe set that is useful in methods where twolabels are used to read four bases. As shown in 202, the A probe islabeled with a first label (identified as C1), the T probe (or U probe,if desirable) is labeled with a second label (C2), the C probe islabeled with both the first and the second label (C1+C2), and the Gprobe is not labeled. As will be appreciated by those in the art, anycombination or variation can be used (e.g. the T probe labeled with C1,the C probe labeled with C2, the A probe labeled with C1+C2, etc.). Insequencing applications utilizing a probe set such as that pictured in202, the presence of the G probe is assumed when no label can bedetected. The labels on probes such as those pictured in FIG. 2 can beany kind of detectable label known in the art as described more fullybelow, and in specific cases, fluorescent labels are used.

As described more fully below, additional detection positions, e.g.multiple detection positions, can be detected in a variety of ways. Inone embodiment, iterative cycles of these methods can be done tosequentially detect additional detection positions. That is, afterligation and detection of the labels present (which allows theidentification of the base at the detection position), the ligatedprobes are released from the array and the process is repeated for a newdetection position. In other embodiments, as more fully described belowand in FIG. 2, 4 colors can be used to identify nucleotides at twodetection positions simultaneously, for example at the “upstream” end ofthe adapter and at the “downstream” end of the adapter. In thisembodiment, the first set of sequencing probes (e.g. the “upstream” set)uses two different labels (e.g. a first and a second label) and thesecond set of sequencing probes (e.g. the “downstream” set) uses twodifferent labels (e.g. a third and a fourth label). As will beappreciated by those in the art, in this embodiment, frequently the“non-ligation” terminus will be blocked such that ligation cannot occurat one terminus. For example, in the probes (204) shown in FIG. 2, the5′ end of the first set is blocked such that ligation at the 5′ endcannot occur, and the same for the 3′ ends of the second set. Thisprevents a probe from the first set hybridizing to the wrong terminus ofthe adapter, which could lead to ambiguity. In other embodiments, alsoas described herein, the present invention allows the identification oftwo detection positions simultaneously, even if not “upstream” and“downstream” of a single adapter. That is, these techniques can be usedto identify detection positions adjacent to two different adapters ofthe concatamer.

In general, the unique labels can be generated in a number of ways. Asshown above, two labels can be used to label 4 probe sets: dye1, dye 2,dye1+2, and nodye. Alternatively, the intensity of the label can be usedto create unique labels. For example, a probe set may comprise uniquelabel1 as dye1 used at 1× intensity, label2 is dye1 used at 2×intensity, label3 is dye used at 10× intensity, and label4 can be nodye.This embodiment can be done in two general ways. In one embodiment, eachprobe can comprise one or more labels; e.g. probe1 has one fluorophoreper probe, probe2 has two fluorophores per probe, and probe3 has 10fluorophores per probe. However, due to both the expense of the dyes andthe crosstalk (including quenching) that can occur with multiple labelsper probe, another embodiment utilizes probe sets such that only aportion of the set is labeled. That is, probe1 can have 10% of the setlabeled with one fluorophore, and the rest are unlabeled (e.g. label1 is0.1× dye), probe2 can have 50% of the set labeled with one fluorophore,and the rest are unlabeled (e.g. label2 is 0.5× dye), and probe3 canhave 100% of the probes labeled. This results in a relative intensitydifference serving as the unique label. As will be appreciated by thosein the art, these methods can also be combined, where different dyes atdifferent intensities are used (e.g. probe1 is dye1 at 10% coverage,probe2 is dye1 at 100% coverage, probe3 is dye2 at 10% coverage, andprobe4 is dye 2 at 100% coverage, etc.). Any and all combinations arecontemplated herein.

In addition, as more fully outlined below, dissociative labels can beused to increase the confidence of a base call; in this embodiment, aread is done (e.g. in the case of fluorophores, an image of the array iscollected) and then the conditions are changed to disassociate one ofthe labels, and a second image is taken.

Thus, sequencing applications using the nucleic acid nanoballs of theinvention can detect more than two bases in a target nucleic acid byutilizing probes that can only hybridize to one side of an adaptor orthe other. For example, in FIG. 2, set 204 is premised along the samelines as set 202, except that with set 204, four different labels areused to distinguish between 8 different nucleotides—i.e., to identifywhich base is present at two different locations in a target sequence.As discussed above, nucleic acid nanoballs of the invention compriserepeating units of target sequence and adaptors. In specific examples ofsequencing applications of the invention, four of the probes in set 204are 3′ probes, i.e., they can hybridize to locations of the targetsequence 3′ to an adaptor, whereas the other four probes are 5′ probesand hybridize only to locations 5′ to an adaptor. Similar to thelabeling scheme of set 202 discussed above, the 5′ probes of set 204 hasan A probe labeled with a first label (C1), a T probe labeled with asecond label (C2), a C probe labeled with the first and second labels(C1+C2) and a G probe that has no label. In addition, the 3′ probes ofset 204 has an A probe labeled with a third label (C3), a T probelabeled with a fourth label (C4), a C probe labeled with both the thirdand fourth label (C3+C4), and again the G probe is unlabeled. Bystructuring the probes in this way, a set such as probe set 204 can beused to identify the nucleotide at two different positions of a targetsequence.

In certain cases, the nucleotides at four different positions of atarget sequence in a nucleic acid nanoball are identified by using fourprobe sets in a single sequencing cycle to read two bases from each sideof an adaptor. One example of such a sequencing application isillustrated in FIG. 6A, which shows an exemplary portion of a nucleicacid nanoball 602 with adaptors on each of the 5′ and 3′ ends (shaded“b”s) and target nucleic acid to be sequenced in between the adaptors(i.e., in between the shaded regions). In addition, sequencing probesare shown that would allow for reading of the four bases from 5′ and 3′of the two adaptors shown in two cycles (again, with optional blockingto prevent ligation at the incorrect end). In the method of sequencingillustrated in FIGS. 6A and 6B, probe sets of the type shown in FIG. 2at 204 are used; however, four probe sets are used in a single reactionto read two bases from each side. In FIGS. 6A and 6B, “G”, “T”, “A” and“C” are specific nucleotide bases and “N”s are universal or degeneratebases. In a first cycle of sequencing, four probes sets 620 are used. Asequencing probe that would identify the G in the target nucleic acidimmediately 3′ to the end of the 5′ adaptor is shown at 604(CNNNNNN-C1/C2). Such a sequencing probe would be part of a first set622: CNNNNNN-C1/C2; ANNNNNN-C1; TNNNNNN-C2 and GNNNNNN (see FIG. 6B forthe probe sets that would be used in each of the two rounds ofsequencing). The sequencing probe that would identify the T in thetarget nucleic acid two bases from the 3′ end of the 5′ adaptor is shownat 606 (NANNNNN‡C1), and would be part of a second set 624: NANNNNN‡C1;NTNNNNN‡C2; NGNNNNN; and NCNNNNN‡C1C2, where the symbol “‡” denotes acleavage site). A broad variety of cleavable moieties are available inthe art of solid phase and microarray oligonucleotide synthesis,including photocleavable moieties (see, e.g., Pon, R. (1993), MethodsMol. Biol. 20:465-496; Verma et al. (1998), Annu. Rev. Biochem.67:99-134; and U.S. Pat. Nos. 5,739,386 and 5,700,642). Again, using a Gprobe in this instance is optional, since the G probe does not have alabel.

A sequencing probe that would identify the C in the target nucleic acidimmediately 5′ to the end of the 3′ adaptor is shown at 612 (NNNNNNG).Such a sequencing probe would be part of a third set 626: NNNNNNG;C3/C4-NNNNNC; C31-NNNNNA; and C4-NNNNNT. The sequencing probe that wouldidentify the A in the target nucleic acid two bases from the 5′ end ofthe 3′ adaptor is shown at 614 (C4‡NNNNTN), and would be part of afourth set 628: C4‡NNNNTN; C3‡NNNNAN; NNNNNGN; and C3C4‡NNNNCN, again,where the symbol “‡” denotes a cleavage site. The first, second, thirdand fourth sequencing probe sets are used together to sequence fourbases at a time in the following manner: Anchor probes are allowed tohybridize to the adaptors in the library constructs after which (orsimultaneously) all four sets of sequencing probes are added and allowedto hybridize to the target nucleic acid. The adjacently-hybridizedanchor probes and sequencing probes may then be ligated to one anotherif the sequencing probe is complementary to the target nucleic acid inthe library construct. An extensive wash is performed to eliminateunligated sequencing probes. Two sequencing probes will ligate to theanchor probes that hybridized to the 5′ adaptor (one sequencing probefrom the first sequencing probe set (604) and one sequencing probe fromthe second sequencing probe set (606)), and two sequencing probes willligate to anchor probes that hybridized to the 3′ adaptor (onesequencing probe from the third sequencing probe set (612) and onesequencing probe from the fourth sequencing probe set (614)). It shouldbe noted that more than one sequencing probe will not ligate to a singleanchor probe, but about half of the 5′ anchor probes will ligate tosequencing probes from the first set, and about half of the 5′ anchorprobes will ligate to sequencing probes from the second set. Similarly,about half of the 3′ anchor probes will ligate to sequencing probes fromthe third set, and about half of the 5′ anchor probes will ligate tosequencing probes from the fourth set.

The fluorescent signal for the first read out in this hypothetical wouldbe C1+C2+C1 from the 5′ side and no color (from the G sequencingprobe)+C4 from the 3′ side. The sequencing reaction mix is thensubjected to cleaving at the “‡” site, eliminating the fluorescentsignal from the sequencing probes interrogating the bases in the targetnucleic acid two nucleotides from the ligation junction (i.e.,sequencing probes from the second and fourth sequencing probe sets). Awash is then performed, and the fluorescent signal is read again. Thefluorescent signal for the second read out in this hypothetical would beC1+C2 from the 5′ side and no color from the 3′ side. That is, thestrong C1 signal contributed by the NANNNNN‡CL sequencing probe (606)and the C4 signal contributed by the C2‡NNNNNTN sequencing probe (614)will have disappeared. The disappearance of a strong C1 signal indicatesthat a T is two bases from the 3′ end of the 5′ adaptor (the Asequencing probe from the second set ligated to the anchor probe). Thedisappearance of the C4 signal indicates that an A is two bases from the5′ end of the 3′ adaptor (the T sequencing probe from the fourth setligated to the anchor probe). The remaining C1+C2 signal indicates thata G is in the first position in the target nucleic acid immediately 3′to the end of the 5′ adaptor (the C sequencing probe from the first setligated to the anchor probe) and that there is no color at all from thethird sequencing probe set indicates that a C is the first base in thetarget nucleic acid immediately 5′ to the end of the 3′ adaptor (the Gsequencing probe from the third set ligated to the anchor probe).

In a second cycle of sequencing in this hypothetical, the third andfourth nucleotides in the target nucleic acid 3′ to the end of the 5′adaptor and the third and fourth nucleotides in the target nucleic acid5′ to the end of the 3′ adaptor are read simultaneously using a secondgroup of four probe sets 630. A sequencing probe that would identify theA in the target nucleic acid three bases 3′ from the end of the 5′adaptor is shown at 608 (NNTNNNN-C2). Such a sequencing probe would bepart of a fifth set 632: NNTNNNN-C2; NNANNNN-C1; NNCNNNN-C1C2 andNNGNNNN. The sequencing probe that would identify the C in the targetnucleic acid four bases 3′ from the end of the 5′ adaptor is shown at610 (NNNGNNN), and would be part of a sixth set 634: NNNGNNN;NNNANNN‡CL; NNNTNNN‡C2 and NNNCNNN‡C1C2, where the symbol “‡” denotes acleavage site. The sequencing probe that would identify the T in thetarget nucleic acid three bases 5′ from the end of the 3′ adaptor isshown at 616 (C3-NNNNANN). Such a sequencing probe would be part of aseventh set 636: C3-NNNNANN; C4-NNNNTNN; C3C4-NNNNCNN; and NNNNGNN. Thesequencing probe that would identify the G in the target nucleic acidfour bases 5′ from the end of the 3′ adaptor is shown at 618(C3C4‡NNNCNNN), and would be part of an eighth set 638: C3C4‡NNNCNNN;C3‡NNNANNN; NNNGNNN; and C4‡NNNTNNN, again, where the symbol “‡” denotesa cleavage site.

As before, the fifth, sixth, seventh and eighth sequencing probe setscan be used together to sequence four bases at a time in the followingmanner: Anchor probes are allowed to hybridize to the adaptors in thelibrary constructs after which (or simultaneously) all four sets ofsequencing probes are added and allowed to hybridize to the targetnucleic acid. The adjacently-hybridized anchor probes and sequencingprobes may be ligated to one another, providing additional hybridizationstability to the sequencing probes complementary to the target nucleicacid. An extensive wash is performed to eliminate unligated sequencingprobes. Two sequencing probes will ligate to the anchor probes thathybridized to the 5′ adaptor (one sequencing probe from the firstsequencing probe set (604) and one sequencing probe from the secondsequencing probe set (606)), and two sequencing probes should ligate tothe anchor probes that hybridized to the 3′ adaptor (one sequencingprobe from the third sequencing probe set (612) and one sequencing probefrom the fourth sequencing probe set (614)).

The fluorescent signal for the first read out in this second round ofsequencing hypothetical would be C2+ no color from the 5′ side and C3+C4from the 3′ side, with C3 in an approximately 2:1 ratio with C4. Thesequencing reaction mix is then subjected to cleaving at the “‡” site, awash is performed, and the fluorescent signal is then re-read. Thefluorescent signal for the second read out in this hypothetical would beC2 from the 5′ side and C3 only from the 3′ side. That is, the no colorsignal contributed by the NNNGNNN sequencing probe (610) and the C3C4signal contributed by the C3C4‡NNNCNNN sequencing probe (618) will havedisappeared. The no change in C2 signal indicates that a C was in thefourth position in the target nucleic acid four nucleotides 3′ from theend of the 5′ adaptor (the G sequencing probe from the sixth set ligatedto the anchor probe). The disappearance of the C4 signal and decreasedrelative intensity of the C3 signal indicates that an G was in thefourth position in the target nucleic acid 5′ from the end of the 3′adaptor (the C sequencing probe from the eighth set ligated to theanchor probe). The no change in the remaining C2 signal indicates thatan A was in the third position in the target nucleic acid 3′ from theend of the 5′ adaptor (the T sequencing probe from the fifth set ligatedto the anchor probe) and remaining C3 signal indicates that a T was inthe third position in the target nucleic acid 5′ from the end of the 3′adaptor (the A sequencing probe from the seventh set ligated to theanchor probe). Though this particular aspect shows use of foursequencing probe sets, two from each of the 5′ and 3′ adaptor, othercombinations may be employed; for example, all four probe sets could beused on the same adaptor, either 5′ or 3′, and the like, though readingfrom 5′ from two different adaptors or reading 3′ from two differentadaptors would not work in this aspect. Further, fifth and sixth labelsmay be used with fifth and sixth sets of sequencing probes to acquiresequence from yet another adaptor or from a different direction on anadaptor being employed with the first and second or third and fourthsets of sequencing probes, and so on with seventh and eighth labels andsequencing sets.

FIG. 3 discloses probes that could be used in yet another embodiment ofthe sequencing methods herein. As in the methods shown and described inFIGS. 6A and 6B, four bases may be read per cycle using four colors andthree images, resulting in four-fold fewer cycles and one-quarter lessimages than with methods used currently in the art. In brief, the methodshown in FIG. 3 reads two bases for each of 5′ and 3′ anchors such asshown in FIG. 6A, but rather than utilizing a cleavable moiety, thedifferent optically-discernable tags have different T_(m)'s and thisproperty is exploited by using discriminating washes between imagingevents, i.e., by dissociating the tags from the sequencing probes. A setof sequencing probes is shown at 302. Each sequencing probe comprises asequencing portion (301, 303, 305, and 307) with a interrogationnucleotide (here at the 1 position, respectively, A, T, C, G), a tail(304, 308, 312, and 316) a tail complement (306, 310, 314 and 318) witheach tail complement comprising a label (309, 311, 313 and 315). Notethat the tail and tail complement (304 and 306) for the “A” sequencingprobe (301) is of a relative length 4×, the tail and tail complement(308 and 310) for the “T” sequencing probe (303) is of a relative length3×, the tail and tail complement (312 and 314) for the “C” sequencingprobe (305) is of a relative length 2×, and the tail and tail complement(316 and 318) for the “G” sequencing probe (307) is of a relative length1× (alternatively, the G probe can be unlabelled). Shown here, both thetails and the tail complements are shown to be of relative length 4×,3×, 2×, and 1×. However, in alternative aspects, the tails may the sameor of similar lengths, and only the tail complements vary in length.Also, in some alternative aspects, the label for one of the sequencingprobes in a set will not be dissociable from the sequencing probe.

Two 5′ sequencing probe sets are used and two 3′ sequencing probe setsare used. The first sequencing probe set will interrogate the first baseimmediately 3′ to the end of the 5′ adaptor (namely, GN₆X₃, CN₆X₅, TN₆X₇and AN₆X₉); the second sequencing probe set will interrogate the secondbase 3′ from the end of the 5′ adaptor (namely, NGN₅X₃, NCN₅X₅, NTN₅X₇and NAN₅X₉); the third sequencing probe set will interrogate the firstbase immediately 5′ to the end of the 3′ adaptor (namely X₃N₆G, X₅N₆C,X₇N₆T and X₉N₆A); and the fourth sequencing probe set will interrogatethe second base 5′ from the end of the 3′ adaptor (namely X₃N₅GN,X₅N₅CN, X₇N₅TN and X₉N₅AN). Here, “G”, “C”, “T” and “A” are specificbases, “N”s are degenerative bases in the sequencing probes, “X”s arebases in the tail portions of the sequencing probes, “Y”s arecomplementary sequences in the tail complements to the “X” sequences inthe tails, and C1, C2, C3 and C4 are different colors (e.g.,fluorophores).

In methods using sequencing probe sets as shown here in FIG. 3, thefirst, second, third and fourth sequencing probe sets are used togetherto sequence four bases at a time: Anchor probes are allowed to hybridizeto the adaptors in library constructs after which (or simultaneously)all four sets of sequencing probes are added, allowed to hybridize tothe target nucleic acid, and then are ligated to theadjacently-hybridized anchor probes. An extensive wash is performed toeliminate unligated sequencing probes. As in the methods described forFIGS. 6A and 6B, two sequencing probes should ligate to anchor probesthat hybridized to the 5′ adaptor (one from the first sequencing probeset and one from the second sequencing probe set), and two sequencingprobes should ligate to anchor probes that hybridized to the 3′ adaptor(one from the third sequencing probe set and one from the fourthsequencing probe set). Again, no more than one sequencing probe willligate to an anchor probe, but about half of the 5′ anchor probes willligate to sequencing probes from the first set, and about half of the 5′anchor probes will ligate to sequencing probes from the second set.Similarly, about half of the 3′ anchor probes will ligate to sequencingprobes from the third set, and about half of the 5′ anchor probes willligate to sequencing probes from the fourth set.

In an embodiment where the G sequencing probe from the first sethybridized to the target nucleic acid and ligated to the 5′ anchor, theT sequencing probe from the second set hybridized to the target nucleicacid and ligated to the 5′ anchor, the A sequencing probe from the thirdset hybridized to the target nucleic acid and ligated to the 3′ anchorand the C sequencing probe from the fourth set hybridized to the targetnucleic acid and ligated to the 3′ anchor, the fluorescent signal wouldbe C1+C2 from the 5′ side and C3+C4 from the 3′ side. The sequencingreaction mix is then subjected to a discriminating wash at a temperaturewhere the short “G” tail complements will be washed away, and thefluorescent signal is then re-read. The fluorescent signal for thesecond read out in this hypothetical would be C2+C3+C4, indicating thatthe C1-associated sequencing probe (the label associated with the firstset of sequencing probes) was a G. Next, a second discriminating wash isperformed at a temperature that would remove the C sequencing probes.Again an image is taken, and the third read out would be C2+C3,indicating that the C4-associated sequencing probe (from the fourth setof sequencing probes) was a C. A third discriminating wash is thenperformed at a temperature that would remove the T sequencing probes.Another image is taken and the last read out is C3, indicating that theC2-associated sequencing probe was a T (the label associated with thesecond set of sequencing probes), and the C3-associated sequencing probeis an A. Again, though this particular embodiment shows use of foursequencing probe sets, two from each of the 5′ and 3′ adaptor, othercombinations may be employed; for example, all four probe sets could beused on the same adaptor, either 5′ or 3′, and the like. Further, fifthand sixth labels may be used with fifth and sixth sets of sequencingprobes to acquire sequence from yet another adaptor or from a differentdirection on an adaptor being employed with the first and second orthird and fourth sets of sequencing probes, and so on with seventh andeighth labels and sequencing sets.

FIG. 4 shows sequencing probe sets that may be useful in still furtherembodiments of the invention. As in the methods shown and described inFIGS. 6B and 3, four bases may be read per cycle using four colors. Incertain embodiments, a single image may be taken to distinguish all fourbases, resulting in a four-fold reduction in the number of images thatmust be acquired overall. In brief, the method shown in FIG. 8 reads twobases for each of 5′ and 3′ anchors such as shown in FIGS. 6B and 3, butrather than utilizing a cleavable moiety or tail complements withdifferent T_(m)'s, each optically-discernable tag, e.g., fluorophore,has 4 different levels of brightness associated with one of thenucleotides A, T, C or G. In this embodiment, two 5′ sequencing probesets are used. The first set will interrogate the first base immediately3′ to the end of the 5′ adaptor (namely, GN₆, CN₆C1, TN₆C1⁺ andAN₆C1⁺²); the second set will interrogate the second base 3′ from theend of the 5′ adaptor (namely, NGN₅, NCN₅C2, NTN₅C2⁺ and NAN₅C2⁺²), thethird set will interrogate the first base immediately 5′ from the end ofthe 3′ adaptor (namely N₆G, C3N₆C, C3⁺N₆T and C3⁺²N₆A); and the fourthset will interrogate the second base 5′ from the end of the 3′ adaptor(namely N₅GN, C4N₅CN, C4⁺N₅TN and C4⁺²N₅AN). As before, “G”, “C”, “T”and “A” are specific bases, “N”s are degenerative bases in thesequencing probes, C1, C2, C3 and C4 are different colors (e.g.,fluorophores), and, e.g., C1, C1⁺ and C1⁺² differ in brightness orintensity of the fluorophore.

In methods using sequencing probe sets as shown here in FIG. 4, thefirst, second, third and fourth sequencing probe sets are used togetherto sequence four bases at a time: Anchor probes are allowed to hybridizeto the adaptors in library constructs after which all four sets ofsequencing probes are added, allowed to hybridize to the target nucleicacid, and then are ligated to the adjacently-hybridized anchor probes.An extensive wash is performed to eliminate unligated sequencing probes.As in the methods described for FIGS. 6B and 3, two sequencing probesshould ligate to anchors that hybridized to the 5′ adaptor (one from thefirst sequencing probe set and one from the second sequencing probeset), and two sequencing probes should ligate to anchor probes thathybridized to the 3′ adaptor (one from the third sequencing probe setand one from the fourth sequencing probe set). Again, no more than onesequencing probe will ligate to each anchor, but about half of the 5′anchor probes will ligate to sequencing probes from the first set, andabout half of the 5′ anchor probes will ligate to sequencing probes fromthe second set. Similarly, about half of the 3′ anchor probes willligate to sequencing probes from the third set, and about half of the 3′anchors will ligate to sequencing probes from the fourth set.

In an embodiment in which the G sequencing probe from the first sethybridized to the target nucleic acid and ligated to the 5′ anchor, theT sequencing probe from the second set hybridized to the target nucleicacid and ligated to the 5′ anchor, the A sequencing probe from the thirdset hybridized to the target nucleic acid and ligated to the 3′ anchorand the C sequencing probe from the fourth set hybridized to the targetnucleic acid and ligated to the 3′ anchor, the fluorescent signal wouldbe C2⁺ from the 5′ side and C3⁺²+C4 from the 3′ side, corresponding to atarget sequence of CA immediately adjacent to the 5′ adaptor (with the Gsequencing probe from the first set providing no color and the Tsequencing probe from the second set providing C2⁺) and TG immediatelyadjacent to the 3′ adaptor (with the A sequencing probe from the thirdset providing C3⁺² and the C sequencing probe from the fourth setproviding C4).

The intensity difference between the fluorophores may be achieved bydiffering concentrations of the A, T, C, G sequencing probes within eachset, or by varying lengths of the sequencing probes within each set(e.g., by using more degenerate or universal bases), or by usingdiscriminatory modifications (e.g., using PNAs or LNAs in varyingamounts) for the sequencing probes in each set. In preferred aspects,the intensity difference is achieved by attaching a different number offluorophores (or other tags), such as, e.g., 0, 1, 2 and 4 fluorophoresper sequencing probe (e.g., zero labels on the G sequencing probe, onelabel on the T sequencing probe, two labels on the A sequencing probe,and four labels on the C sequencing probe), or 0, 1, 3 and 6-9fluorophores per sequencing probe (e.g., zero labels on the G sequencingprobe, one label on the T sequencing probe, three labels on the Asequencing probe, and six to nine labels on the C sequencing probe). Asyet another alternative, the same could be achieved with dyes with thesame emission wavelength but with different brightnesses. Although inthe embodiment pictured in FIG. 4, the C probe is associated with thefluorophore with a 1× brightness, in some aspects the C probe isassociated with the brightest fluorophores (e.g., fluorophore with the4× brightness) as it has been observed that C has minimal cross talkwith other bases. G is shown in FIG. 8 to be the nucleotide that is notassociated with a fluorophore, which is preferred in many aspects as ithas been observed that G is prone to cross talk. T, in some aspectswould be the 1× probe (e.g., C1) and A would be the 2× probe (e.g.,C1⁺). Overall, that is, a scheme of C>A>T>G would be used in someaspects. In still further embodiments, different levels of intensitiescan be achieved by varying the number of probes within a set thatcomprise a particular label. For example, if A probes should showgreater intensity than T probes, one way to achieve this distinction isby labeling a larger relative number of the A probes in the set with alabel than T probes, such that in a sequencing reaction overall, alarger percentage of the A probes will be labeled than the T probes, andthus the signal associated with a base call of “A” will have a higherintensity than the signal associated with a base call of “T”.

Other aspects of the technology may be employed using labels ofdifferent intensities. In one implementation, four bases in one positionmay be read with two colors using two different intensities of the twocolors. For example, a probe set where the A probe is labeled with C1,the T probe is labeled with C1+, the C probe is labeled with C2 and theG probe is labeled with C2+ may be employed in reactions where one baseis read per reaction. Sequencing by synthesis methods may employ thisscheme where one position is read per cycle. In implementations wheretwo bases are read per reaction, one 5′ from an adaptor and one 3′ fromthe same or a different adaptor, an exemplary probe set may include a 5′A probe labeled with C1, a 5′ T probe labeled with C1+, a 5° C. probelabeled with C2 and a 5′ G probe labeled with C2+; and a 3′ A probelabeled with C3, a 3′ T probe labeled with C3+, a 3° C. probe labeledwith C4 and a 3′ G probe labeled with C4+.

In some embodiments, sequencing methods of the invention utilize invaderoligonucleotides. FIG. 11 is a schematic illustration of a method forcPAL sequencing using invader oligonucleotides, where the invaderoligonucleotides provide selective removal of each anchorprobe/sequencing probe complex in a multiplexed reaction. A portion of alibrary construct is shown at 1102, comprising two adaptors (shaded andindicated at 1103 and 1107) with target nucleic acid to be sequenced1105 and 1109 (indicated by “B”s). A first anchor probe/sequencing probecomplex is indicated at 1104, with the sequencing probe portion at 1112and the ligation indicated by a “.”. A second anchor probe/sequencingprobe complex is indicated at 1108, with the sequencing probe portion at1114 and the ligation between the two probes indicated by a “.”. Allsequencing probes may come from the same set of sequencing probes, shownhere as 1120. Invader oligonucleotides are indicated at 1106 and 1110.In FIG. 5, “G”, “T”, “A” and “C” denote specific sequences, “N”s areuniversal or degenerate bases, n is equal to zero to 10, and C1, C2, C3and C4 correspond to four different colored labels, e.g., fluorophores.Though only two adaptors are shown, multiple bases from multipleadaptors (rather than only the two seen here) may be interrogated at onetime in this multiplexed cPAL reaction. To determine which sequencingprobe is positive for each anchor probe, a discriminative removal ofeach anchor probe/sequencing probe complex is used using displacement(de-hybridization from the library construct) by invaderoligonucleotides.

Invader oligonucleotides are identical or substantially identical toportions of the adaptors in the library constructs, and arecomplementary to the anchor probes. The invader oligonucleotides invadeand destabilize the hybrid between the anchor probe/sequencing probe andthe adaptor/target nucleic acid in the library construct 1102. Invaderoliognucleotides can be structured in a number of ways to be disruptiveof the anchor probe/sequencing probe:adaptor/target nucleic acidhybrids. For example, the invader oligonucleotides may have greaterhomology and/or have a longer stretch of homology to the anchor probesthan do the adaptors. In some aspects, the anchor probe may include anoverhang on the opposite end of the strand from the ligation site withthe sequencing probe that is not complementary to the adaptor, but iscomplementary to the invader oligonucleotide. Also, the anchor probesmay be engineered to have less than perfect homology to the adaptors,yet have perfect homology with the invader oligonucleotides. In yetanother alternative, the invader oligonucleotides may employ PNA or LNAchemistry to make the hybrids with the anchor probes/sequencing probesmore stable. In preferred aspects such as shown here, the invaderoligonucleotides comprise degenerative bases (designated N_(n)) thatprovide homology to the sequencing probe ligated to the anchor probeallowing for increased homology to the anchor probe/sequencing probecomplex, further destabilizing the anchor probe/sequencingprobe:adaptor/target nucleic acid hybrid.

In methods using sequencing probe sets as shown in FIG. 11, anchorprobes are allowed to hybridize to the adaptors in library constructsafter which the set of sequencing probes is added, allowed to hybridizeto the target nucleic acid, and the sequencing probes are then ligatedto the adjacently-hybridized anchor probes. An extensive wash isperformed to eliminate unligated sequencing probes. In this example, onesequencing probe should ligate to each anchor probe. An image is thentaken. In a hypothetical where an A sequencing probe from the set ofsequencing probes hybridized to the target nucleic acid and ligated tothe anchor probe at the 5′ end of the library construct (producingstructure 1104) and a C sequencing probe from the set of sequencingprobes hybridized to the target nucleic acid and ligated to the anchorprobe at the 3′ end of the library construct (producing structure 1108),the first image would show a C1+C3 signal. Next, a first invaderoligonucleotide (e.g., that shown at 1106) is added to the sequencingmix under conditions that allow the invader oligonucleotide todestabilize the hybrid between the anchor probe/sequencing probe 1104and the library construct 1102. A wash is then performed, removing thehybridized anchor probe/sequencing probe 1104 and the invaderoligonucleotide 506 from the target nucleic acid. When the next image isthen taken, only a C3 signal remains, indicating that there was a Timmediately adjacent 3′ to the 5′ adaptor 1103 and that there is a Gimmediately adjacent 5′ to the 3′ adaptor 1107.

As an alternative to using four fluorophores, in certain aspects of thepresent invention, two fluorophores may be used to read four bases. Forexample, a probe set such as Probe A-C1, Probe C C1+C2, Probe G-nofluorophore and Probe T-C2 is useful in such techniques where, forexample, the A probe is labeled with a first fluorophore, the T probe islabeled with a second fluorophore, the C probe is labeled with both thefirst fluorophore and the second fluorophore, and the G probe is notlabeled such that a G is deduced if there is no fluorescence emitted. Inaddition, a probe set may allow for the reading of two bases at a timefrom two different adaptors with two different sequencing probe sets. Insuch a scheme, the discrimination of the invader oligonucleotide coupledwith the use of different labels for sequencing from different adaptorsincreases the confidence level of the sequence read. For example, infirst probe set the A probe may be labeled with a first fluorophore, theT probe may be labeled with a second fluorophore, the C probe may belabeled with both the first fluorophore and the second fluorophore, andthe G probe may not be labeled such that a G is deduced if there is nofluorescence emitted from either the first fluorophore or the secondfluorophore (e.g., for a set comprising sequencing probes interrogatingthe second base from the ligation junction, 3′ to 5′: NANNNN-C1,NCNNNNC1C2, NTNNNNC2, and NGNNNN). For the 3′ set, the A probe islabeled with a third fluorophore, the T probe is labeled with a fourthfluorophore, the C probe is labeled with both the third fluorophore andthe fourth fluorophore, and the G probe is not labeled such that a G isdeduced if there is no fluorescence emitted from either the thirdfluorophore or the fourth fluorophore (e.g., for a set comprisingsequencing probes interrogating the second base from the ligationjunction, 3′ to 5′: C3-NNNNAN, C3C4NNNNCN, C4NNNNTN, and NNNNGN).

In yet another alternative, two bases may be read at a time from thesame adaptor using the same anchor probe, the same invaderoligonucleotide and two sequencing different probe sets, where, forexample, in the first probe set the A probe is labeled with a firstfluorophore, the T probe is labeled with a second fluorophore, the Cprobe is labeled with both the first fluorophore and the secondfluorophore, and the G probe is not labeled such that a G is deduced ifthere is no fluorescence emitted from either the first fluorophore orthe second fluorophore (e.g., for a set comprising sequencing probesinterrogating the second base from the ligation junction, 3′ to 5′:NANNNN-C1, NCNNNNC1C2, NTNNNNC2, and NGNNNN), and where in the secondprobe set, A probe is labeled with a third fluorophore, the T probe islabeled with a fourth fluorophore, the C probe is labeled with both thethird fluorophore and the fourth fluorophore, and the G probe is notlabeled such that a G is deduced if there is no fluorescence emittedfrom either the first fluorophore or the second fluorophore (e.g., for aset comprising sequencing probes interrogating the second base from theligation junction, 3′ to 5′: NNANNN-C1, NNCNNNC1C2, NNTNNNC2, andNNGNNN). Again, such an approach reduces the number ofhybridization/ligation cycles and the number of images in half,providing a near two-fold savings in cost and a two-fold savings intime. A preferred approach is to not score (label) the G probe, as G isknown to have cross talk with A and T probes, on the other hand, the Cprobe has been observed to have the least cross talk, such thatpreferably it is the C probe that is labeled with two fluorophores.

As with FIG. 11, FIG. 7 is a schematic illustration of yet anotherembodiment of cPAL sequencing, using anchor probes, sequencing probesand invader oligonucleotides. A portion of a library construct is shownat 701, having one adaptor (shaded) with target nucleic acid to besequenced (indicated by “B”s). An anchor probe/sequencing probe complexis indicated at 702, with the sequencing probe portion at 606 and theligation indicated by a “.”. Although only one adaptor, anchorprobe/sequencing probe complex and one invader oligonucleotide areshown, it should be understood that, as in FIG. 11, two, four or moresets of probes and invaders may be used in a multiplexed reaction. As inFIG. 7, all sequencing probes may come from the same set of sequencingprobes, shown here as 710. The invader oligonucleotide is indicated at703. As before, “G”, “T”, “A” and “C” denote specific sequences, “N”sare universal or degenerate bases, n is equal to zero to 10, and C1, 21,C2, C3 and C4 correspond to four different colored labels, e.g.,fluorophores. As in FIG. 11, in FIG. 7 a discriminative removal of eachanchor probe/sequencing probe ligated structure 702 is used usingdisplacement by invader oligonucleotides 703 to determine whichsequencing probe is ligated to which anchor probe; however, the anchorprobe and invader oligonucleotide in this example have loops (704 and705, respectively) that are complementary to one another, but that donot have homology to the adaptor within the library construct. The loopsincrease the relative homology of the anchor probe/sequencing probe tothe invader oligonucleotide, and decrease the relative homology of theanchor probe/sequencing probe to the adaptor and target nucleic acidportions of the library construct. In addition, as described infra, theloops may be useful for other purposes as well. In addition, the invaderprobe includes a series of degenerative bases (indicated by “N_(n)”)that bind with the sequencing probe portion of the anchorprobe/sequencing probe complex further destabilizing the hybrid with thelibrary construct.

In methods using anchor probes, sequencing probe sets and invaderoligonucleotides as shown here in FIG. 7—as in FIG. 11—anchor probes areallowed to hybridize to the adaptors in library constructs after whichthe set of sequencing probes is added, allowed to hybridize to thetarget nucleic acid, and the sequencing probes are then ligated toadjacently hybridized anchor probes. An extensive wash is performed toeliminate unligated sequencing probes. In the aspect shown here, onesequencing probe should ligate to each anchor probe. An image is thentaken. In a hypothetical where an A sequencing probe from the set ofsequencing probes hybridized to the target nucleic acid and ligated tothe anchor probe (to produce structure 702), and, for example, a Tsequencing probe from the set of sequencing probes hybridized to thetarget nucleic acid and ligated to another anchor probe (not shown) andanother A sequencing probe from the set of sequencing probes hybridizedto the target nucleic acid and ligated to yet another anchor probe (notshown), the first image would show a C1 (x2)+C2 signal. A first invaderoligonucleotide (e.g., shown at 603) is then added to the sequencing mixunder conditions that allow the invader oligonucleotide to destabilizethe hybrid between the anchor probe/sequencing probe 702 and the libraryconstruct 701 and to form a complex with the anchor probe/sequencingprobe. A wash is then performed, removing the hybrid anchorprobe/sequencing probe/invader oligonucleotide complex. When the nextimage is then taken, a C1+C2 signal remains, indicating that there wasan A one base immediately adjacent the 3′ end of the adaptor (shaded). Asecond round of invasion and imaging would remove, e.g., the C2-labeledsequencing probe, leaving only a C1 signal, showing that there was an Aone base immediately adjacent the 3′ end of another adaptor, and thatthere is a T one base immediately adjacent the 3′ end of the last,uninvaded adaptor.

FIG. 8 is a schematic illustration of yet another exemplary libraryconstruct, anchor probe, sequencing probe and invader oligonucleotideuseful in certain methods of the claimed invention. A portion of alibrary construct is shown at 812, having one adaptor (shaded) withtarget nucleic acid to be sequenced (indicated by “B”s). An anchorprobe/sequencing probe complex is indicated at 814, with the sequencingprobe portion at 816, the anchor probe portion at 813 (complementary toan adaptor in the library construct and to a portion of the targetnucleic acid), a tail portion of the anchor probe at 815 (complementaryto a tail portion 818 of the invader oligonucleotide, seen at 817) and aligation site indicated by a “.”. Although only one adaptor/invaderoligonucleotide anchor probe/sequencing probe complex is shown, itshould be understood that two, four or more sets of anchor probes andinvader oligonucleotides may be used in a multiplexed reaction. Allsequencing probes may come from the same set of sequencing probes, shownhere as 830 (where the base to be interrogated is 4 bases from theligation junction). The invader oligonucleotide has an anchor portion819 (complementary to an adaptor in the library construct) and a tailportion 818. The invader oligonucleotide/anchor probe/sequencing probecomplex is indicated at 811.

The anchor portion of the invader oligonucleotide 713 serves tostabilize the anchor probe/sequencing probe complex, so that the anchorprobe may comprise a sequence of degenerate nucleotides that providescomplementarity to a portion of the target nucleic acid, allowing for ashift of the site of ligation such that more bases can be read or readwith more confidence further from the 5′ end of the adaptor in thelibrary construct. However, the greater complementarity between theinvader oligonucleotide 817 and the adaptor probe/sequencing probecomplex 714 will allow selective disruption of the adaptorprobe/sequencing probe complex 814 from the library construct 812. Asdescribed previously, the anchor probes are allowed to hybridize to theadaptor probes in library constructs after which the set of sequencingprobes is added, allowed to hybridize to the target nucleic acid, andthe sequencing probes are then ligated to the adjacently-hybridizedanchor probes. An extensive wash is performed to eliminate unligatedsequencing probes. One sequencing probe should ligate to each anchorprobe. An image is then taken. Next, a first invader oligonucleotide isadded to the sequencing mix under conditions that allow the invaderoligonucleotide to destabilize the hybrid between the anchorprobe/sequencing probe and the library construct. A wash is thenperformed, removing the hybridized anchor probe/sequencing probe and theinvader oligonucleotide from the target nucleic acid. When the nextimage is then taken, the label from the sequencing probe that has beenselectively removed with the invader oligonucleotide should not bepresent.

As before, “G”, “T”, “A” and “C denote specific sequences, “N”s areuniversal or degenerate bases, n is equal to zero to 10, and C1, C2, C3and C4 correspond to four different colored labels, e.g., fluorophores.“B”s in the library construct denote bases in the target nucleic acidthat are to be sequenced. “B” in the sequencing probe denotes theinterrogation base. In addition, the complementary tails in the anchorprobe and the invader oligonucleotide, if desired, allow for theinclusion of cleavable sites (uracils, restriction sites, photocleavablesites) for specific removal of a anchor probe/sequencing probe complex,if desired.

In FIG. 8, the invader oligonucleotide 817 has a loop. In the aspectshown in FIG. 8, the loop in the invader oligonucleotide can be used tovary the properties of the invader oligonucleotide/anchorprobe/sequencing probe complex. For example, as shown in FIG. 8, theloop can be used as a molecular “hook” such that an additionaloligonucleotide (a “loop binding oligonucleotide” shown at 820) withcomplementarity to the loop in the tail portion of the invaderoligonucleotide can bind the complex. The loop binding oligonucleotidecan associate a non-nucleotide molecule(s) with the complex, such as anadditional label (shown here at 821), a quenching moiety, a moiety thatincreases intensity of the label on the sequencing probe, a moiety thatshifts the frequency of the label on the sequencing probe, an entitythat allows for the complex to be captured (e.g., by biotin or anotherligand, or a magnetic bead), and the like. The loop 705 in the invaderoligonucleotide shown at 703 in FIG. 7 may serve similar functions.

For any of the sequencing methods described herein, methods of detectingand identifying sequencing probes are dependent on the types of labelsused with those sequencing probes. Such labels and methods of detectionare well known in the art and are described for example in U.S.application Ser. Nos. 11/679,124; 11/981,761; 11/981,661; 11/981,605;11/981,793; 11/981,804; 11/451,691; 11/981,607; 11/981,767; 11/982,467;11/451,692; 12/335,168; 11/541,225; 11/927,356; 11/927,388; 11/938,096;11/938,106; 10/547,214; 11/981,730; 11/981,685; 11/981,797; 12/252,280;11/934,695; 11/934,697; 11/934,703; 12/265,593; 12/266,385; 11/938,213;11/938,221; 12/325,922; 12/329,365; 12/335,188 and 12/359,165, all ofwhich are hereby incorporated by reference in their entirety for allpurposes and particularly for all disclosure related to sequencingprobes, labeled sequencing probes, methods of making labeled andunlabeled sequencing probes, and methods of detecting sequencing probes.

The present specification provides a complete description of themethodologies, systems and/or structures and uses thereof in exampleaspects of the presently-described technology. Although various aspectsof this technology have been described above with a certain degree ofparticularity, or with reference to one or more individual aspects,those skilled in the art could make numerous alterations to thedisclosed aspects without departing from the spirit or scope of thetechnology hereof. Since many aspects can be made without departing fromthe spirit and scope of the presently described technology, theappropriate scope resides in the claims hereinafter appended. Otheraspects are therefore contemplated. Furthermore, it should be understoodthat any operations may be performed in any order, unless explicitlyclaimed otherwise or a specific order is inherently necessitated by theclaim language. It is intended that all matter contained in the abovedescription and shown in the accompanying drawings shall be interpretedas illustrative only of particular aspects and are not limiting to theembodiments shown. Unless otherwise clear from the context or expresslystated, any concentration values provided herein are generally given interms of admixture values or percentages without regard to anyconversion that occurs upon or following addition of the particularcomponent of the mixture. To the extent not already expresslyincorporated herein, all published references and patent documentsreferred to in this disclosure are incorporated herein by reference intheir entirety for all purposes. Changes in detail or structure may bemade without departing from the basic elements of the present technologyas defined in the following claims.

1.-21. (canceled)
 22. A method for determining identities of nucleotidesat detection positions of a plurality of different nucleic acidtemplates, said method comprising i) performing sequencing reaction onthe plurality of different templates using two distinguishablefluorescent labels; ii) determining the identities of nucleotides atdetection positions based on the presence or absence of each of the twodistinguishable fluorescent labels.
 23. The method of claim 22 whereinthe sequencing reaction comprises producing, for the differenttemplates, a labeled polynucleotide comprising sequence complementary tothe template nucleic acids.
 24. The method of claim 23 wherein thelabeled polynucleotide is a produced by ligating a sequencing probe andan anchor probe, wherein the anchor probe hybridizes to a sequenceshared by the plurality of different template nucleic acids.
 25. Themethod of claim 22 comprising: (a) providing an array comprisingsingle-stranded nucleic acid templates disposed at positions on asurface; (b) for a plurality of said nucleic acid templates, determiningthe identity of a first nucleotide in the nucleic acid template by: i)binding a complementary nucleotide to said first nucleotide, ii)detecting, at the position on the surface occupied by the nucleic acidtemplate, the presence or absence of fluorescent signal(s) associatedwith the complementary nucleotide; wherein 1) detecting a firstfluorescent signal and not a second fluorescent signal at the positionidentifies the complementary nucleotide as a nucleotide selected from A,T, G and C; 2) detecting the second fluorescent signal and not the firstfluorescent signal at the position identifies the complementarynucleotide as a nucleotide selected from A, T, G and C that is differentfrom the nucleotide selected in (1); 3) detecting both the firstfluorescent signal and the second fluorescent signal at the positionidentifies the complementary nucleotide as a nucleotide selected from A,T, G and C that is different from nucleotides selected in (1) and (2);and 4) detecting neither the first fluorescent signal nor the secondfluorescent signal at the position identifies the complementarynucleotide as a nucleotide selected from A, T, G and C that is differentfrom the nucleotides selected in (1), (2) and (3); iii) deducing theidentity of the first nucleotide in the nucleic acid template based onthe identity of the complementary nucleotide.
 26. The method of claim 25wherein the step of binding the complementary nucleotide to the firstnucleotide is part of a sequencing by extension reaction.
 27. The methodof claim 25 wherein the step of binding the complementary nucleotide tothe first nucleotide comprises hybridizing an oligonucleotide comprisingthe complementary nucleotide to the single-stranded nucleic acidtemplate in a sequencing by ligation reaction.
 28. The method of claim25 wherein the nucleic acid templates comprise adaptors.
 29. The methodof claim 26 wherein the nucleic acid templates comprise adaptors. 30.The method of claim 29 wherein the nucleic acid templates compriseadaptors.
 31. The method of claim 28 wherein the nucleic acid templatesare formed from a plurality of genomic fragments.
 32. The method ofclaim 29 wherein the nucleic acid templates are formed from a pluralityof genomic fragments.
 33. The method of claim 30 wherein the nucleicacid templates are formed from a plurality of genomic fragments.
 34. Themethod of claim 31 wherein the genomic fragments are human genomic DNA.35. The method of claim 32 wherein the genomic fragments are humangenomic DNA.
 36. The method of claim 33 wherein the genomic fragmentsare human genomic DNA.
 37. The method of claim 22 comprising: providinga nucleic acid template comprising an anchor sequence and, adjacent theanchor sequence, a target nucleic acid sequence; hybridizing an anchorprobe to the anchor sequence; extending the anchor probe in one or morecycles of sequencing-by-synthesis using a set of nucleotides thatconsists of: (i) first nucleotides comprising a first label; (ii) secondnucleotides comprising a second label; (iii) third nucleotidescomprising both the first label and the second label; and (iv) fourthnucleotides comprising neither the first label nor the second label,wherein the first label and the second label are distinguishable fromeach other; and detecting the presence or absence of the first labeland/or the second label added in each cycle of sequencing-by-synthesisto determine the sequence of the target nucleic acid sequence.
 38. Themethod of claim 37 wherein the nucleic acid template is immobilized on asurface.